Two JSON blobs, one with the main product, a second one that can be output later on the page that clearly relates itself to the first one as a related product.

two-products-best.json

<script type="application/ld+json">{
    "@context": "https://schema.org",
    "@graph": [
        {
            "@type": "Organization",
            "@id": "https://example.com/#organization",
            "name": "Yoast",
            "url": "https://example.com/",
            "sameAs": [
                "https://www.facebook.com/yoast",
                "https://www.linkedin.com/company/yoast-com/",
                "https://en.wikipedia.org/wiki/Yoast",
                "https://twitter.com/yoast"
            ],
            "logo": {
                "@type": "ImageObject",
                "@id": "https://example.com/#logo",
                "url": "https://example.com/wp-content/uploads/2019/03/Yoast_Logo_tagline_Large_RGB.png",
                "caption": "Yoast"
            },
            "image": {
                "@id": "https://example.com/#logo"
            }
        },
        {
            "@type": "WebSite",
            "@id": "https://example.com/#website",
            "url": "https://example.com/",
            "name": "one.wordpress.test",
            "publisher": {
                "@id": "https://example.com/#organization"
            },
            "potentialAction": {
                "@type": "SearchAction",
                "target": "https://example.com/?s={search_term_string}",
                "query-input": "required name=search_term_string"
            }
        },
        {
            "@type": "ItemPage",
            "@id": "https://example.com/product/vneck-tee/#webpage",
            "url": "https://example.com/product/vneck-tee/",
            "inLanguage": "en-US",
            "name": "Vneck Tshirt - one.wordpress.test",
            "isPartOf": {
                "@id": "https://example.com/#website"
            },
            "image": {
                "@type": "ImageObject",
                "@id": "https://example.com/product/vneck-tee/#primaryimage",
                "url": "https://example.com/wp-content/uploads/2019/03/vneck-tee.jpg",
                "caption": ""
            },
            "primaryImageOfPage": {
                "@id": "https://example.com/product/vneck-tee/#primaryimage"
            },
            "datePublished": "2019-03-27T15:16:56+00:00",
            "dateModified": "2019-04-09T09:08:35+00:00",
            "description": "Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor",
            "breadcrumb": {
                "@id": "https://example.com/product/vneck-tee/#breadcrumb"
            }
        },
        {
            "@type": "BreadcrumbList",
            "@id": "https://example.com/product/vneck-tee/#breadcrumb",
            "itemListElement": [
                {
                    "@type": "ListItem",
                    "position": 1,
                    "item": {
                        "@type": "WebPage",
                        "@id": "https://example.com/",
                        "url": "https://example.com/",
                        "name": "Home"
                    }
                },
                {
                    "@type": "ListItem",
                    "position": 2,
                    "item": {
                        "@type": "WebPage",
                        "@id": "https://example.com/shop/",
                        "url": "https://example.com/shop/",
                        "name": "Products"
                    }
                },
                {
                    "@type": "ListItem",
                    "position": 3,
                    "item": {
                        "@type": "WebPage",
                        "@id": "https://example.com/product/vneck-tee/",
                        "url": "https://example.com/product/vneck-tee/",
                        "name": "Vneck Tshirt"
                    }
                }
            ]
        },
        {
            "@type": "Product",
            "@id": "https://example.com/product/vneck-tee/#product",
            "name": "Vneck Tshirt",
            "url": "https://example.com/product/vneck-tee/",
            "image": {
                "@id": "https://example.com/product/vneck-tee/#primaryimage"
            },
            "description": "Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.",
            "sku": 83,
            "offers": [
                {
                    "@type": "Offer",
                    "price": "18.00",
                    "priceValidUntil": "2020-12-31",
                    "priceSpecification": {
                        "price": "18.00",
                        "priceCurrency": "EUR",
                        "valueAddedTaxIncluded": "false"
                    },
                    "priceCurrency": "EUR",
                    "availability": "https://schema.org/InStock",
                    "url": "https://example.com/product/vneck-tee/",
                    "seller": {
                        "@id": "https://example.com/#organization"
                    }
                }
            ],
            "aggregateRating": {
                "@type": "AggregateRating",
                "ratingValue": "4.50",
                "reviewCount": 2
            },
            "review": [
                {
                    "@id": "https://example.com/product/vneck-tee/#comment-5",
                    "datePublished": "2019-04-09T09:10:12+00:00",
                    "description": "What a nice turtle shirt.",
                    "reviewRating": {
                        "@type": "Rating",
                        "ratingValue": "4"
                    },
                    "author": {
                        "@type": "Person",
                        "name": "Tim"
                    }
                },
                {
                    "@id": "https://example.com/product/vneck-tee/#comment-6",
                    "datePublished": "2019-04-09T09:10:29+00:00",
                    "description": "Awesome shirt",
                    "reviewRating": {
                        "@type": "Rating",
                        "ratingValue": "5"
                    },
                    "author": {
                        "@type": "Person",
                        "name": "Patrice"
                    }
                }
            ],
            "brand": {
                "@type": "Organization",
                "name": "Turtle"
            },
            "manufacturer": {
                "@type": "Organization",
                "name": "Turtle"
            },
            "mainEntityOfPage": {
                "@id": "https://example.com/product/vneck-tee/#webpage"
            }
        }
      ] }</script>
      <script type="application/ld+json">
      "@context": "https://schema.org",
    "@graph": [
        {
            "@type": "Product",
            "@id": "https://example.com/product/vneck-tee/#product2",
            "name": "Vneck Tshirt 2",
            "url": "https://example.com/product/vneck-tee/#2",
            "image": {
                "@id": "https://example.com/product/vneck-tee/#primaryimage"
            },
            "description": "Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo.",
            "sku": 83,
            "offers": [
                {
                    "@type": "Offer",
                    "price": "18.00",
                    "priceValidUntil": "2020-12-31",
                    "priceSpecification": {
                        "price": "18.00",
                        "priceCurrency": "EUR",
                        "valueAddedTaxIncluded": "false"
                    },
                    "priceCurrency": "EUR",
                    "availability": "https://schema.org/InStock",
                    "url": "https://example.com/product/vneck-tee/",
                    "seller": {
                        "@id": "https://example.com/#organization"
                    }
                }
            ],
            "aggregateRating": {
                "@type": "AggregateRating",
                "ratingValue": "4.50",
                "reviewCount": 2
            },
            "review": [
                {
                    "@id": "https://example.com/product/vneck-tee/#comment-5",
                    "datePublished": "2019-04-09T09:10:12+00:00",
                    "description": "What a nice turtle shirt.",
                    "reviewRating": {
                        "@type": "Rating",
                        "ratingValue": "4"
                    },
                    "author": {
                        "@type": "Person",
                        "name": "Tim"
                    }
                },
                {
                    "@id": "https://example.com/product/vneck-tee/#comment-6",
                    "datePublished": "2019-04-09T09:10:29+00:00",
                    "description": "Awesome shirt",
                    "reviewRating": {
                        "@type": "Rating",
                        "ratingValue": "5"
                    },
                    "author": {
                        "@type": "Person",
                        "name": "Patrice"
                    }
                }
            ],
            "brand": {
                "@type": "Organization",
                "name": "Turtle"
            },
            "manufacturer": {
                "@type": "Organization",
                "name": "Turtle"
            },
			"isRelatedTo": {
				"@id": "https://example.com/product/vneck-tee/#product"
			}
        }
    ]
}</script>