Add sku in ajax search results

funtions.php

<?php 

add_filter('yith_wcas_suggestion', 'yith_wcas_suggestion', 10, 2); 
function yith_wcas_suggestion( $suggestion, $product ){ 
$sku = $product->get_sku(); 
if( ! empty( $sku ) ){ 
$suggestion['sku'] = '<span class="sku">SKU: '. $product->get_sku().'</span>'; 
}

return $suggestion; 
}