The get_admin_page_parent() WordPress PHP function retrieves the parent file of the current admin page.
Usage
$parent_page = get_admin_page_parent('example-submenu-page');
Parameters
- $parent_page (string) – Optional. The slug name for the parent menu (or the file name of a standard WordPress admin page). Default: ”.
 
More information
See WordPress Developer Resources: get_admin_page_parent()
Examples
Add a submenu page under the “Settings” menu
function my_plugin_menu() {
    add_submenu_page(
        'options-general.php',
        'My Plugin Settings',
        'My Plugin',
        'manage_options',
        'my-plugin-settings',
        'my_plugin_settings_page'
    );
}
add_action('admin_menu', 'my_plugin_menu');
function my_plugin_settings_page() {
    $parent_page = get_admin_page_parent('my-plugin-settings');
    echo 'The parent page is: ' . $parent_page;
}
Add a submenu page under the “Posts” menu
function my_custom_submenu() {
    add_submenu_page(
        'edit.php',
        'My Custom Submenu',
        'My Custom Submenu',
        'manage_options',
        'my-custom-submenu',
        'display_custom_submenu'
    );
}
add_action('admin_menu', 'my_custom_submenu');
function display_custom_submenu() {
    $parent_page = get_admin_page_parent('my-custom-submenu');
    echo 'The parent page is: ' . $parent_page;
}
Add a submenu page under the “Pages” menu
function my_page_submenu() {
    add_submenu_page(
        'edit.php?post_type=page',
        'My Page Submenu',
        'My Page Submenu',
        'manage_options',
        'my-page-submenu',
        'display_page_submenu'
    );
}
add_action('admin_menu', 'my_page_submenu');
function display_page_submenu() {
    $parent_page = get_admin_page_parent('my-page-submenu');
    echo 'The parent page is: ' . $parent_page;
}
Add a submenu page under the “Appearance” menu
function my_theme_submenu() {
    add_submenu_page(
        'themes.php',
        'My Theme Submenu',
        'My Theme Submenu',
        'manage_options',
        'my-theme-submenu',
        'display_theme_submenu'
    );
}
add_action('admin_menu', 'my_theme_submenu');
function display_theme_submenu() {
    $parent_page = get_admin_page_parent('my-theme-submenu');
    echo 'The parent page is: ' . $parent_page;
}
Add a submenu page under a custom top-level menu
function my_custom_menu() {
    add_menu_page(
        'My Custom Menu',
        'My Custom Menu',
        'manage_options',
        'my-custom-menu',
        'display_custom_menu'
    );
    add_submenu_page(
        'my-custom-menu',
        'My Custom Submenu',
        'My Custom Submenu',
        'manage_options',
        'my-custom-submenu',
        'display_custom_submenu'
    );
}
add_action('admin_menu', 'my_custom_menu');
function display_custom_menu() {
    echo 'This is the main page of My Custom Menu.';
}
function display_custom_submenu() {
    $parent_page = get_admin_page_parent('my-custom-submenu');
    echo 'The parent page is: ' . $parent_page;
}