For some reason my by author disappeared and I cant turn it back on. I know where I want to put it on single.php at the end of the post, but I can't figure out what code I have to put in for it to display.
The property on the object for author is post_author. You can access it like this in the loop where $post is your WP_Post object.
$author = $post->post_author;
If you want to display it: