How to get menu location in wp_update_nav_menu hook

get_nav_menu_locations will give you menu IDs keyed by location which should correspond to the $id also passed with wp_update_nav_menu.

add_action('wp_update_nav_menu', function ($id, $data = NULL){

    foreach( get_nav_menu_locations() as $location => $menu_id ){
        if( $id == $menu_id ){
            echo 'location is ' . $location;
        }
    }

}, 10, 2);