Custom taxonomies

You can use get_the_terms( int|WP_Post $post, string $taxonomy ) . See Codex detail here.

$my_terms = get_the_terms( get_the_id(), 'regionen' );
if ( ! empty( $my_terms ) ) {
    if ( ! is_wp_error( $my_terms ) ) {
        echo '<ul>';
            foreach( $my_terms as $term ) {
                if($term->parent == 0){
                    echo '<li><a href="' . get_term_link( $term->slug, 'regionen' ) . '">' . esc_html( $term->name ) . '</a></li>'; 
                }
            }
        echo '</ul>';
    }
}