Used to view all available information on a registered nick. This will show whether it is registered, when it was registered, to whom, when it was last used, and various options that are set for the nick. Opers may be able to see more information than regular users.
/msg nickserv info benny
This is a good command to use to check if a nick that interests you is registered or to see when a friend's nick was last used. You should info your own nick so you can see what others will find out if they do so.