Return custom product in ajax call loop

Yes, you can query products by their ids and display them as ajax response. You code just needs a little revision. Perhaps you could try something along these lines,

public function display_search_result(){ 

  $skus = urldecode($_POST['sku_universel']); 
  $skus = explode(',',$sku);
  $product_ids = array();

  // you can use native woocommerce function to get the product ids
  foreach($skus as $sku){
    $product_id = wc_get_product_id_by_sku($sku);
    if ( is_int($product_id) ) { 
      $product_ids[] => $product_id;
    }
  } 

  $args = array( 
    'post_type'      => 'product', // product, not products
    'post_status'    => 'publish', 
    'post__in'       => $product_ids,
    'posts_per_page' => 100 // change this based on your needs
  );
  $ajaxposts = new WP_Query( $args );

  $response="";

  if ( $ajaxposts->posts ){ 
    while ( $ajaxposts->have_posts() ) { 
      $ajaxposts->the_post(); 
      $response .= wc_get_template_part( 'content', 'product' ); // use WooCommerce function to get html
    } 
  } else { 
    // handle not found by yourself or
    // perhaps do_action( 'woocommerce_no_products_found' ); could do the trick?
  }

  echo $response;
  exit;

}