does Shadow of Chernobyl Steam key activate on GoG?
CD Keys found in SoC + Clear Sky on Steam should might activate up on GOG.
You'll have to try your luck.
Not everybody's had all their keys works.
See RCSample's post below about SoC Steam not activating on GOG:
https://www.cheapassgamer.com/topic/328533-bundle-stars-thread-ending-all-stars-lords-of-the-fallen-bundles/?p=12628984
For SoC on Steam, two ways to find your CD key - after you've downloaded the game.
A You can check Regedit - it should be in there.
Look under Computer\HKEY_LOCALMACHINE\SOFTWARE\Wow6432Node\GSC Game World\STALKER-SHOC.
B. Boot SoC game up; start up MP portion to look at servers; click on the XXXX-XXXX-XXXX-XXXX in upper-right hand corner for the CD key. That's your CD key to activate on GOG.
C. Once you did either A or B, go to the GOG Steps.
For Clear Sky on Steam - Right click on game in Steam Library; check CD Key; get the key.
GOG Steps - Take your CD key from Steam; get on your GOG account; and activate that key in their Redeem on GOG section.
I did try - and yes, they will redeem on GOG, if you follow through with it.
You punch in the key, and it will show you what will activate; it will asks you if you want to do so; and then you decide to follow through (or not).
Of course, I didn't redeem those Steam CD keys on GOG.
I already redeemed retail keys of SoC + Clear Sky on GOG.
EDIT:
Post edited to reflect people like RCSample, who unfortunately ain't been able to get their keys activated onto GOG.