I want all my games in one place. Steam is that place. Can i redeem GOG version of Witcher 2 in steam in any way? All i can find is how to redeem Steam version on GoG.

Thanks.

No, you can't.

However, You can add non-Steam games to Steam so that you can track your achievements and get the Steam interface. You know, in case you're into that sort of thing.

pigulici already answered you, and vidsgame answered a bit more... Long story short, you cannot redeem GOG codes on Steam. Steam is an entirely separate platform, and GOG and Steam are direct competitors. GOG is trying to earn more customers' trust by offering certain Steam games to be redeemed on GOG, but Steam will most likely never return the favor.