Source

File: wp-includes/customize/class-wp-customize-nav-menu-item-setting.php

protected function get_type_label( $item ) {
		if ( 'post_type' === $item->type ) {
			$object = get_post_type_object( $item->object );
			if ( $object ) {
				$type_label = $object->labels->singular_name;
			} else {
				$type_label = $item->object;
			}
		} elseif ( 'taxonomy' === $item->type ) {
			$object = get_taxonomy( $item->object );
			if ( $object ) {
				$type_label = $object->labels->singular_name;
			} else {
				$type_label = $item->object;
			}
		} elseif ( 'post_type_archive' === $item->type ) {
			$type_label = __( 'Post Type Archive' );
		} else {
			$type_label = __( 'Custom Link' );
		}
		return $type_label;
	}