How to show actual category ID

You can show the category ID with the following code:

add_action( 'single_product_end', 'my_show_category_id');

function my_show_category_id($post) {
   $terms = wp_get_post_terms( $post->ID, 'al_product-cat', array( "fields" => "ids" ) );
   if (!empty($terms[0])) {
      echo intval($terms[0]);
   }
}

This will show the first product category ID on the bottom of the product page.