From what I learned last night, it looks like Epik’s blog comment form may be the standard Genesis 2 (HTML 5). So far, I haven’t found a switch in the WordPress settings to turn it off and on. Most of the commenting settings are in the WP dashboard under Settings>Discussion. But nothing for email replies.
I found a plug-in called “Comment Notifier.” It creates a checkbox, but also has lots of other comment settings I don’t need. I was hoping to do this without an additional plug-ins.