Show menu on page with all sub-pages and sub-sub-pages of that page

You can use get_page_children function to retrieve all sub pages

$the_query = new WP_Query( array( 'post_type' => 'page', 'posts_per_page' => -1 ) );
$children = get_page_children( get_the_ID(), $the_query->query() );

if ( !empty( $children ) ) {
    foreach ( $children as $child ) {
        // render menu
    }
}