在一个页面wordpress上显示辅助导航

I have this bit of code in my header:

        <?php if (has_nav_menu('sub-header-menu', 'responsive')) { ?>
            <?php wp_nav_menu(array(
                'container'       => '',
                'menu_class'      => 'sub-header-menu',
                'theme_location'  => 'sub-header-menu')
                ); 
            ?>
        <?php } ?>

And I need something that will make it only show on the blog page and the children for that page (i.e the categories).. I'm not great with PHP but I guess this would be something simple

Just add a page Id of your blog page in you condition.

$parentPageId = is_subpage();
if (has_nav_menu('sub-header-menu', 'responsive') &&
   (is_page( $blogPageId ) || $parentPageId == $blogPageId))

You can alos check your page using slug.

is_page( 'blog' ) 

Function to get Parent Page Id if exists.

function is_subpage() {
    global $post;
    if ( is_page() && $post->post_parent ) {
        return $post->post_parent;
    } else {
        return false;
    }
}

Find out the ID of the blog page $blogid = 123 (for example) and then check with if ($page->ID == $blogid) { /*show menu*/ }