Wordpress - List all the tags from a custom post type
wp_get_object_terms will have your answer.
wp_get_object_terms( $post_ids, 'post_tag', $optional_args );
There is also get_the_terms which is simpler but also gets the job done.
get_the_terms( $id, 'post_tag');
get_the_term_list(), the different is that
the_tags() has the default put in for
Watch them in