Add featured image to Genesis single post with full control of options. Also a cleaner version with no image link.

functions.php

<?php
 
// Add featured image to single posts.
add_action ( 'genesis_entry_content', 'aafcm_show_featured_image_single', 1 );
function aafcm_show_featured_image_single() {
	global $post;
    if ( is_page() )
        return; // Make pages act normal
 
    //setup thumbnail image args to be used with genesis_get_image();
    $size = 'thumbnail'; // Change this to whatever add_image_size you want
    $default_attr = array(
            'class' => "alignright attachment-$size $size",
            'alt'   => $post->post_title,
            'title' => $post->post_title,
        );
 
    // This is the most important part!  Checks to see if the post has a Post Thumbnail assigned to it. You can delete the if conditional if you want and assume that there will always be a thumbnail
    if ( has_post_thumbnail() && is_single() ) {
        printf( '<a href="%s" title="%s">%s</a>', get_permalink(), the_title_attribute( 'echo=0' ), genesis_get_image( array( 'size' => $size, 'attr' => $default_attr ) ) );
    }
}

functions1.php

<?php
 
// Add featured image to single posts.
// Cleaner approach. No image link.
add_action ( 'genesis_entry_content', 'aafcm_show_featured_image_single', 1 );
function aafcm_show_featured_image_single() {
    if ( has_post_thumbnail() && is_single() ) {
        $img = genesis_get_image( array( 'size' => 'thumbnail', 'attr' => array( 'class' => "alignright" ) ) );
        printf( '%s', $img );
    }
}