I am extending discussion from one another article posted on the same website → Where should I use post_class()?.

This is the portion from content-single.php →

Where should I put the post-class? in the h2 tag that will print the title or on the parent article tag, which has one other div,which is a sibling to h2, title class?

  <h4><?php the_title(); ?></h4>
  <p><?php the_content(); ?></p>

I browsed this link, but still, I could not get the clarity → /

REQUIRED: Could not find post_class. See: post_class <div id="post-" >