List admins of a user group?

I was trying to add a user to a user group that I’m currently in.

With

pts adduser -user MyFriend -group OneOfMyGroups

I got

ts: Permission denied ; unable to add user MyFriend to group OneOfMyGroups

This makes sense as I may not be the admin of OneOfMyGroups.

Now I wish to find out who are. How do I do this?