There is no defined way of telling. You will connect to the 'nearest' server. This can be the server that responds quickest - and could be a server across a WAN link, not necessarily the closest on your network segment. This can also be affected by what ZENworks container policies you have configured. For example, of server TEST1 is in the UK.TEST container, and a user logs into the UK.TEST container, a container policy will stop tree-walking and automatically connect the user to server TEST1 (your workstations have to imported into NDS for container policies to work).
If your network guys are clever enough, they can also define a GNS (Get Nearest Server) list on the routers to stop GNS requests across WANs. But, ultimately, the server that responds will be a server with an NDS replica on it for authentication purposes.
I have noticed, by the way, that the GET NEAREST SERVER set command on the Novell servers is pants as network settings (as described above) will override this and set the setting back to ON. Dunno why?