jamesdio

OK. So I will answer for others…

First of all, edit functions.php and add this code:

function register_my_menus() {
  register_nav_menus(
    array(
      'menu-footer' => __( 'Menu in the footer' ),
    )
  );
}
add_action( 'init', 'register_my_menus' );

The code above registers new menu, name of the new menu is in my case: menu-footer

Next add these lines:

function my_wp_nav_menu_args( $args = '' ) {

// Primary menu location
if( 'primary' == $args['theme_location'] ) {

if( is_user_logged_in() ) {
$args['menu'] = 'logged-in-menu';
} else {
$args['menu'] = 'logged-out-menu';
}
return $args;
}

// Secondary menu location
if( 'menu-footer' == $args['theme_location'] ) {

if( is_user_logged_in() ) {
$args['menu'] = 'menu-informacyjne';
} else {
$args['menu'] = 'menu-informacyjne';
}
return $args;
}
}
add_filter( 'wp_nav_menu_args', 'my_wp_nav_menu_args' );

The first menu (primary) is different for logged in/logged out users.
The second menu (menu-footer) is always visible for logged/non logged users.

I edited one more file: footer.php in my theme folder and added this line:
<?php wp_nav_menu( array( 'theme_location' => 'menu-footer' ) ); // this is my menu-footer>

Now everything works fine. All edited files are in child theme folder of course…

Any idea?

Thanks for answer. Now I know.