In Minecraft Vanilla SMP, having access to the server, can I somehow retrieve the position of an offline player?
Download and run it, choose File → Open, go to your Minecraft server directory, find
players directory, and then select the name of player you want, for example
You should see something like this:
You need to go to "Pos", and there you have it, coords of player you wanted.
Just double click any to edit it.