How can I view my steam keys for steam games ?

Why would you need to see them? You can only see them on games that somehow require you to enter the key.

"only few games have it", that seems about right, not all of them provide keys. Why do you need the keys anyway?

You can't, to my knowledge. It's not (as I understand) the Steam key you're viewing when Steam gives that option.

This is probably what you're thinking of. It only occurs for some games and like I say, that's not a Steam key. It's the GFWL key I think.

Exactly! Most games don't have keys since they are meant to be used in game, probably to unlock DLCs or something, they are not the steam keys you use to get the game. Those after you use them they disapear, since it's not like it can be used later.
The only one I have that has those keys is Dragon Age: Origins - Ultimate Edition.

for example ,key for cogs ?

I'm pretty sure there used to be an option after right clicking a game in your library, I remember needing to check the keys for my games a year back or so -- but can't seem to find it now

you only can see it for some games that have multiplayer or 3rd part games who needs and independent code-check (for example, GTA IV have a serial code for two reason, if exist something strange in a multiplayer game and for Games for Windows can check your game if is original)

Aye. You can't. Which is annoying if you have a bunch of different bundle/game keys from various locations and want to figure out which keys you've activated and which you havn't.
):