How to add Featured Image to Parallax/Llorix One Posts

Before editing any files, make sure that you're using a child theme. Now copy your /content-single.php file to your child theme, and find the following line of code:

<?php the_content(); ?>

Just add the following line above it:

<?php
	if ( has_post_thumbnail() ) {
		the_post_thumbnail();
	} 
?>

Save the file, and you're good to go.