To determine whether the process is still running on the server you'd have to login and run "ps -ef" and look through the running processes (or grep for more specific information if you know it). Sometimes if a session gets detached from a workstation it is still alive on the server but you have no way of reconnecting (unless you set it up for that beforehand).
There ARE utilities that let you run things from one session and detach then reattach again from same workstation or even another workstation.
If what you opened was a terminal window in X so that you could run a command from command line you should use the "screen" utility. You can see a discussion of screen here:
If what you ran was an actual X application and not a terminal under X there are equivalents which are discussed in this thread: