TOPIC: How do I activate the event cancellation feature?

I turned on the cancellation feature on in the "user panel" tab in events, but nothing shows up.

Hello. You need to enable it PER EVENT. Within the event, there is a User Panel tab where you can enable/disable cancellations, editing, etc... and put deadlines and fees for doing so if needed.

Where does the cancellation feature appear? Do I have to enable it in community builder as well?

In the event user tab on the front end, a cancel column appears but there is no cancel button.

It has nothing to do with Community Builder. In the DT Reg User Panel, if you see a Cancel column, but not button... that means cancellation is NOT enabled for that event... or if it is, the cancellation deadline given in the event has passed.