The radiator cap is on the radiator, if you have a radiator cap. Some makes and models don't have a radiator cap. The radiator hoses are attached to the radiator on one end. The radiator is at the front of engine compartment.
You check and add coolant at the coolant reservoir. Any cap that is a pressure cap, you have to be careful when removing. The coolant reservoir is in the picture. Give me a second, I forgot the picture.