There's no built in functionality to do this. There may be a plugin but I don't know of one.
UNSOLVED How to moderate guest topics and replies?
the checkbox is disabled.
That checkbox would enable guests to moderate your forum. As it says right there,
privileges can be granted
The table grants that ability to the certain group
Thanks a lot for your reply.
Actually, I want Admin to moderate all the topics / replies by guests before they appear in the forum.
There's a post approval queue for that. ACP -> Settings -> Post -> Posting Restrictions
Thanks a lot. problem solved.