Where to use Post class in a real theme, title, content or parent div or article tag?

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 → https://developer.wordpress.org/reference/functions/post_class/

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