Hi,

Try to add this code snippet to the functions.php file in the child theme to achieve that

add_action( 'woocommerce_before_shop_loop_item_title', 'custom_before_title' );
function custom_before_title() {

    global $product;

    if ( $product->get_sku() ) {
        echo $product->get_sku();
    }

}

Regards