Список страниц по произвольному полю

1. https://codex.wordpress.org/Class_Reference/WP_Query

Simple Custom Field Query:
Display posts where the custom field key is ‘color’, regardless of the custom field value:
$query = new WP_Query( array( 'meta_key' => 'color' ) );

2. https://codex.wordpress.org/Function_Reference/get_posts

Custom Field Parameters
Show posts associated with a certain custom field. Following example displays posts from the ‘product’ post type that have meta key ‘featured’ with value ‘yes’, using ‘meta_query’:

$args = array(
	'post_type' => 'product',
	'meta_query' => array(
		array(
			'key' => 'featured',
			'value' => 'yes',
		)
	)
 );
$postslist = get_posts( $args );