Returns the names or objects of the taxonomies which are registered for the requested object or object type,
such as a post object or post type name.

Example:

$taxonomies = get_object_taxonomies( ‘post’ );

This results in:

Array( ‘category’, ‘post_tag’ )

function get_object_taxonomies( $object, $output = 'names' ) {
	global $wp_taxonomies;

	if ( is_object( $object ) ) {
		if ( 'attachment' === $object->post_type ) {
			return get_attachment_taxonomies( $object, $output );
		}
		$object = $object->post_type;
	}

	$object = (array) $object;

	$taxonomies = array();
	foreach ( (array) $wp_taxonomies as $tax_name => $tax_obj ) {
		if ( array_intersect( $object, (array) $tax_obj->object_type ) ) {
			if ( 'names' === $output ) {
				$taxonomies[] = $tax_name;
			} else {
				$taxonomies[ $tax_name ] = $tax_obj;
			}
		}
	}

	return $taxonomies;
}