Adding the code snippet in your functions.php file of the child theme will automatically have the featured image appear on single posts.

genesis-featured-image-action.php

<?php //<= remove this
/* Code to Display Featured Image on top of the post */
add_action( 'genesis_before_entry', 'featured_post_image', 8 );
function featured_post_image() {
  if ( ! is_singular( 'post' ) )  return;
	the_post_thumbnail('post-image');
}