render-page-links.php

<?php
add_action( 'genesis_entry_footer', 'tj_subpage_navigation' );
/**
 * Adds page links to the descendants of page ID 6.
 *
 */
function tj_subpage_navigation() {
    //* Return early if not on a page or if on the front page
    if ( ! is_page() || is_front_page() )
        return;

    $greatest_ancestor = 6; // Change this number to the ID of your parent/grandparent page

    tj_page_navigation_links( $greatest_ancestor );
}