Create A Forum - Support Forums

In Admin > Registration > Settings put a checkmark in:   "Notify administrators when a new member joins"
You will get an email when a new member registers.

Also if you have it set to Admin Approval you should see a link and notice at the top of the forum telling you there are new members waiting approval.    See attachment -  you just click where it says "one member" and it'll take you directly into Admin where you can approve them.