Follow the example code below, if you are using WordPress default post. For custom post type the query will be different.
<?php
$args = array(
'category_name' => 'parent_category_slug+featured_category_slug', // change the category slug as your own
);
$query = new WP_Query($args);
if($query->have_posts()):
while($query->have_posts()): $query->the_post(); ?>
<h4><?php the_title(); ?></h4>
<?php
endwhile; // main loop
wp_reset_postdata();
endif; // have posts
?>