I downloaded the game, and I do not think I have a multiplayer cd key.
I would like one.

Thanks.

You need to contact support to get your multiplayer key.
Click on support, at the top of the page.
Then Neverwinter Nights Diamond.
Then on the right hand side, click on " I can't find solution for my problem"
Then where it says "Problem Type" Hit the down arrow and select " Multiplayer Key Request."

Here's the link: https://www.gog.com/support/contact/technical_issues_with_games/neverwinter_nights_diamond_edition

NWN2 gives you a CD key automatically. NWN1 gives you a generic one and then you can request a user-specific one (which is kind of nice if you want to play 2 players together in your home).

Expect up to a few days to get the code, although it can go faster.