Get tags for post_type

Question

It should work:

global $wpdb;

// set the target relationship here
$post_type="post";
$taxonomy = 'tag';

$terms_ids = $wpdb->get_col( $wpdb->prepare( "
SELECT
    tt.term_id
FROM
    {$wpdb->term_relationships} tr,
    {$wpdb->term_taxonomy} tt,
    {$wpdb->posts} p
WHERE 1=1
    AND tr.object_id = p.id
    AND p.post_type="%s"
    AND p.post_status="publish"
    AND tr.term_taxonomy_id = tt.term_taxonomy_id
    AND tt.taxonomy ='%s'
", $post_type, $taxonomy ) );

// here you are
$terms = get_terms( $taxonomy, array(
'include' => $terms_ids,
'orderby' => 'name',
'order' => 'ASC'
) );

It will get your tag terms for a specific custom post type. Then you can do:

foreach( $terms as $tag ) {
    echo '<li class="type-tag">' . $tag->name . '</li>'; 
}

to show your tags on a list.