I've bought a game but i dont know how to view it's key help pls!

Can you elaborate? What key?

I don't think the Witcher needs a key does it, it's just an optional thing? I don't think it does anything now?

If you do need a key for something then I think you need to contact support: http://www.gog.com/support/contact

The game should be in your shelf read to download, if that's what you're looking for.

I looked on the Witcher forum and found this:

http://www.gog.com/forum/the_witcher/game_registration

LOL - I was marked with the solution to that thread! I forgot there used to be a registration key with the game. As noted though, that is no longer valid.

I need key to activate it on steam because i have all my games there And support dont want to answer me((

This isn't a steam key reseller. You won't get a key. What you get from a purchase here is the installers.

ok i got it((

GOG sells DRM free copies. Meaning that you can simply download the installer/install the game and play it. You can also back-up your installer. Also you don't need to have a client (like steam) running in the background.

i like steam)

You can LIKE steam, but you'll LOVE GOG. Customer support is exemplary, and trust me, DRM free is always better than with DRM

You won't get a Steam key from GOG, but if you really want to have the game in your Steam collection, you can add it as a non-Steam game:

https://support.steampowered.com/kb_article.php?ref=2219-YDJV-5557

Will adding non steam games that have a steam variant enable steam works features like COOP and achievements?

AFAIK no.