My forum is set up so that it requires manual approval of all new registrations.  I think I used to get an email when somebody registered but I'm I'm. not getting them now.  If I don't check in the admin panel very regularly, I miss them.  I have looked and I[m sure it's there somewhere but can't find where to turn it on.  

A while back, we created a notifications area in for ACP items like this. You will want to check your configuration in ACP -> Notification bell -> Notification Settings. Please note that these settings are independent for each administrator so everyone will need to configure them how they would like.

I'm missing it.  I can 't find anything that says notification bell.  Where is it?

It's the bell icon in the top-right...

OK...I found it. and email is selected. but. I'm. not getting them.  

Are you getting other emails from your site?  I’m curious if your email provider might not be delivering your mail or marking it as spam. 

Also please check within email errors in System>Email to see if anything is showing there