Genesis is an excellent framework but certain parts of the documentation can be a little lacking. If you want to customise your single post template, you can do the following
Create a file in your child theme folder called single.php
Make sure the last line in this file is the following:
genesis();
Use the Genesis theme hooks and filters to manipulate your markup. The visual theme hook guide is an excellent resource for this. See: https://genesistutorials.com/visual-hook-guide/
So, if you wanted to modify the entry content, you could do something like this:
remove_action('genesis_entry_content', 'genesis_do_post_content');
add_action( 'genesis_entry_content', 'custom_entry_content' ); // Add custom loop
function custom_entry_content() {
//Custom Entry Content
}
This is merely a starting point for modifying your code but there are many useful hooks and filters. All of the markup modification in Genesis is handled through hooks and filters so if you're trying to change the post meta for example, there'll be a filter for that.