You can either use the NAMES #channel command to get that info for all nicks on a given channel or you can use WHOIS nick to get that info for nick on each channel he is on.
In the case of NAMES the response will be a 353 numeric and the nicks will be listed with the appropriate status prefixes before their nick (eg. @+nick1 @nick2 nick3).
For WHOIS you want to check numeric 319, which will list the channels that the specified nick is on, prefixed by status symbols (eg. @+#chan1 @#chan2 #chan3).
See the relevant IRC RFCs (1459 and 2812) or a raw IRC connection for the precise format of the responses.
Note 1: If you aren't on a given channel with a given nick you probably won't be able to see their status/prefix unless you have certain usermodes usually reserved for opers/admins on a server.
Note 2: Some servers will only provide the 'highest' status prefix in the 353/319 responses. For instance a nick who is both opped and voiced on a channel may appear as @nick when you would expect him to appear as @+nick. This is exactly as stupid as it seems and fortunately these servers are rare nowadays.
