//создаем новую колонку
add_filter( 'manage_pages_columns', 'yourtheme_manage_pages_columns' );
function yourtheme_manage_pages_columns( $columns ){
	$columns['post_modified'] = 'Дата редакт.';
	return $columns;
}
//заполняем
add_action( 'manage_pages_custom_column', 'yourtheme_manage_pages_custom_columns', 10, 2 );
function yourtheme_manage_pages_custom_columns($column_name, $post_id){
	if( $column_name === 'post_modified' ){
		$post = get_post($post_id);
		echo $post->post_modified;
	}
}
//добавляем возможность сортировки
add_filter( 'manage_edit-page_sortable_columns', 'yourtheme_manage_pages_sortable_columns' );
function yourtheme_manage_pages_sortable_columns( $sortable_columns ){
	$sortable_columns['post_modified'] = [ 'post_modified', true ]; // true  = desc
	return $sortable_columns;
}