The room where the key is is directly above the "main entry chamber" (the big one with 4 doors right near the beginning). You have to go all the way through the temple, as the bridges are out. You'll eventually reach a point where you need to double-clawshot your way across the missing bridge using those desert-helicopter-basket things. The key is in a tiny room with a big fan in the floor (same fan that's in the ceiling of the main entry room). You can stop the fan with a switch and jump back down through the hole to get back to the main room of the temple, and onward to the boss.
You get it in the sky temple when you beat the mini boss.
in the temple in the sky
Argorok the Dragon
When you beat the mid-boss, from the city in the sky.
The Snowpeak Ruins, the Temple of Time and the City in the Sky
you defeat the mini boss in the lakebed temple and the mini boss in the city in the sky
The thing is, you can't but, you can get a hookshot in the water temple and two hookshots in the sky temple.
you get the second clawshot after you beat the sky temple's mini boss (note the mini boss is a beast known as an aeralfos) thereby getting the double clawshot
Clawshot to his tail then put the iron boots on to drag him down. After that you clawshot from one floating plant to another until you're behind him after he breathes fire. Then clawshot to his back and hit him.
the first one is in the water temple and the second one is in the city in the sky
you need to get both clawshots. you should find the other one in the sky temple. you can use an online walkthrough if you're lost.
There is no "super clawshot" but there is a double clawshot which you can get after you defeat the mini-boss in the city in the sky. Hope this helps!