Functions file
//* One. Register the menu(s) using the init action hook NOT after_theme_setup
//* Two. Hook the menu into a theme hook location ( You could replace the 2nd
//* step with the template code which displays the menu however this is not best
//* practice when modifying Genesis and reserved for parent theme development)
//* Simply change the genesis_after_header hook to the correct hook location you want to display your menu.
//* You can also change the container class (nav-menu) to match the existing Genesis nav menu class or you
//* would need to add a lot of CSS if you use a unique class.
function register_additional_genesis_menus() {
register_nav_menu( 'third-menu' ,
__( 'Third Navigation Menu' ));
}
add_action( 'init', 'register_additional_genesis_menus' );
add_action( 'genesis_after_header', 'add_third_nav' );
function add_third_nav() {
wp_nav_menu( array(
'theme_location' => 'third-menu',
'container_class' => 'genesis-nav-menu' ) );
}