While I have no experience with Genesis, I imagine that the child topics work just like the child topics for all other topics. As documented, a child topic is created by using a
Template: Line to the header style.css, which specifies the directory name of the parent topic:
/* Theme Name: Genesis Child Theme Template: genesis */
By defining the "template" for a theme, WordPress works like
get_template_directory() You know that you need to use the directory of this topic for the path or the URL.