Not quite sure what you want!
If you /whois nickname
then you can see what channels that person is in. You must their nickname to perform a /whois on them.
If a user is in channels that are set to +s
(Secret) or +p
(Private) then you cannot see the channel names. There is no way around this unless you're an IRC Operator, in which case, ask your server administrator. If you're a user, you will not be allowed to do this.
Other than that you need to explain what you need a little more for us to understand it