According to the FAQ:

DLC Installation
To download and install additional language packets and free DLC you need to register the game. The easiest way to do this is to use the "Start The Witcher 2" shortcut located on your desktop and to select the "Register game" option in the launcher. Then follow the instructions in the registration window:
- Log in or create a new account
- Enter your Product Activation Code
After registering the game select the “Downloadable content” option and enter your DLC activation code, which you can find on separate DLC leaflets. Additional Downloadable Content will then be unlocked.



I bought the Witcher 2 from GoG. I've preloaded and waiting for release. I do not see the above mentioned Product Activation Code anywhere. Can someone please tell me where I should look for it?

No, that's for the CD-KEY mate.

It should be in the e-mail you received from GOG when you preordered the game.

It will be on the game's launcher.

My question is will the DLC activation code you put in, will that be the same as the Product activation code, or will we receive that some other time?

No, the DLC for example is either roche's jacket if you got the collectors or the pre-order incentive from retailers. The GOG version does not come with any DLC.

The DLC activation codes are probably for the horse armour crap that you can get from other retailers. (ie. Swordman suit, Alchemist suit, etc.) Registering the game likely provides access to the DLC like the quest that CDPR has promised, no DLC activation codes required. (Troll troubles?)

That's probably already in the game. You just need to register your serial key to activate it.

Thanks for the answers. At first I simply did not see the CD-Key in my email. Now I saw it :)