Add the following code to the end of your Genesis child theme's functions.php file. Read full guide here: https://wp-me.com/display-featured-image-genesis-child-themes/

functions.php

/* Display featured image before single post title */
add_action( 'genesis_before_entry', 'featured_post_image', 8 );
function featured_post_image() {
  if ( ! is_singular( 'post' ) )  return;
	the_post_thumbnail('post-image');
}