The IRC Protocol Specification: A Guide to Not Being Annoyed

2.1: Whois

A request to identify a user, often used to gather information about the user's location, operating system, and other details.

Example:

/whois <username>

Response:

Server: example.com
Name: JohnDoe
Version: 1.0
Server-Name: IRCdude
Server-Machine: localhost
Server-Address: 192.168.0.1
Server-Port: 6667
End of /whois

For more information on other commands, see:

Commands | Whois Queries