Stand at the front left (driver's-side) corner of your car, and you should be able to see it, although if you have your stock air box, there is a good chance that it's in the way.
It's a tight fit, but if you stick your hand down there, you should be able to loosen it, and the radiator coolant will drain out directly below the petcock. Just make sure the engine is cold and you have something underneath to catch the coolant.
