/whois cn
cn = client number, you can see it by the looking on the scoreboard (screen).
As an example, if you were on the server at the time that screen was taken, you could have typed /whois 1 and then you'd see my IP. Next time you see them on a server, just look for their client numbers and type that command.
If you want to make the player's cn more/less visible on the scoreboard, you can use /cncolumncolor and then a number of 1-9 to make it stand out. [EDIT: apparently you can use "0" too. weird]
cn = client number, you can see it by the looking on the scoreboard (screen).
As an example, if you were on the server at the time that screen was taken, you could have typed /whois 1 and then you'd see my IP. Next time you see them on a server, just look for their client numbers and type that command.
If you want to make the player's cn more/less visible on the scoreboard, you can use /cncolumncolor and then a number of 1-9 to make it stand out. [EDIT: apparently you can use "0" too. weird]