Untitled

add_action('marketking_dashboard_head', function(){
    ?>
    <script>
        jQuery(document).ready(function(){
            jQuery('._sku_field').remove();
        });
    </script>
    <style type="text/css">
        ._sku_field{
            display: none !important;
        }
    </style>
    <?php
});
add_action('marketking_after_save_product', function($product_id, $vendor_id){
    $custom_sku_here = 'SKU'.$product_id;
    update_post_meta($product_id, '_sku', $custom_sku_here);
}, 10, 2);