My CD Key is stating that is already in use, i tried support here.. but since i did not get my game through GOG says i have no game to register CD key... anything else i can do?
i have not seen a place where i can add my game here ....

If you have a physical copy of the game then the serial number should be somewhere - in the manual, probably.

If you brought the game from another digital site, contact them.

If you're using an illegal copy, then sayonara. If you didn't buy it here, why do you expect you'd be able to add it here ?

Not illegal copy from gamestop app..
Well i know i can add games onto steam account from cd keys that i have not bought over steam... just need to add via cd key... thats why i thought maybe i could add it here.. but eh.. guess not.. thanks for the reply tho..

NWN Diamond ships with a generic key for personal use - you should be able to request a new (multiplayer) key from Gamestop.