I originally sent in a support ticket ages ago for a nwn cd key, and I got one. Now reinstalling the game I need it again but I can't find the old support ticket anywhere on this site? I still have the email they sent where they said something like:

Hi,

This is an automated message.
Your support request "Need a multiplayer key" has been received. It has been assigned ticket number <redacted>.

If you want to tell us more about this issue, please answer this email.

We will do our best to help you.

Regards,

GOG.com Support

How do I access this ticket to see my old cd key?

As far as i know you cant access old tickets.
The strange thing is a key for a game like Don't starve shows up on your gamepage, but a key like Neverwinter Night doesn't. I thinky your best call is just to request a key again (or the same one) and this time save it good.