Where can I find complete documentation on nslookup?

[Kevin Darcy]

Here's the only documentation you need: "nslookup sucks, use dig instead".

For dig, you can use -x followed by the IP address. You might also want 
to add "ptr" to the command line (because some versions of dig default 
to a query type of "any" on -x queries), unless you're sure you're 
talking to a server that's guaranteed to have the relevant data.

E.g. dig -x 192.168.1.2 ptr

                                                                        
                        - Kevin