Does somebody know how to see which game my Steam Code is for? (Without showing it here ^^)

Nope, there isn't.
The only way to find out is to use it.

That's not possible on Steam.

Nope :)

I only saw that option on Origin.

No. You can only try it, but you would redeem it at the same time, if you don't own the game yet.
Or you find someone who already owns everything at Steam..he could tell you without using it. :D

If you own the game, then you will found it the name after trying to activate it.