Program.cs

using System;

using NetTopologySuite.Features;
using NetTopologySuite.IO;

using Newtonsoft.Json.Linq;

namespace Sample
{
    internal static class Program
    {
        private static void Main(string[] args)
        {
            const string geojsonFeature = @"
{
  ""type"": ""Feature"",
  ""geometry"": {
    ""type"": ""Point"",
    ""coordinates"": [125.6, 10.1]
  },
  ""properties"": {
    ""name"": ""Dinagat Islands""
  }
}";
            var f = new GeoJsonReader().Read<Feature>(geojsonFeature);
            Console.WriteLine(f.Geometry);

            const string arbitraryJson = @"
{
  ""someArbitraryString"": ""foo""
}";
            var x = JObject.Parse(arbitraryJson);
            Console.WriteLine(x.GetValue("someArbitraryString"));
        }
    }
}

Sample.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp1.1</TargetFramework>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="NetTopologySuite.IO.GeoJSON" Version="1.15.0-pre015" />
    <PackageReference Include="Newtonsoft.Json" Version="10.0.3" />
  </ItemGroup>
</Project>