$menus = wp_get_nav_menus();

foreach ( $menus as $menu /** @var WP_Term $menu */ ) {
    echo '<h2>' . $menu->name . '</h2>';
    $menu_items = wp_get_nav_menu_items( $menu->term_id );
    if ( ! empty( $menu_items ) ) {
        echo '<ul>';
        foreach ( $menu_items as $menu_item ) {
            echo '<li><a href="' . $menu_item->url . '">' . $menu_item->title . '</a></li>';
        }
        echo '</ul>';
    }
}