Are you using a Flow or something else as the process engine for this catalog item?
In a Flow, I believe you can dot-walk to the record pretty easily and add the contents of that variable to the email notification.
If using a traditional workflow or other type of process engine, with a "classic" "email notification" triggering on the RITM table input, you'll need to write a mailscript that glides to the RITM and grabs the variable contents, and prints them to the email notification.
Having said that, I'm assuming you're referring to the "Summary of item being approved:" section of the approval email.
If not (if you are referring to a portal widget), there are going to be other ways to do this -- however they all probably involve a glide to the RITM table, specifically to get the info it's looking for.
