To check the cats you'll need to pull them off the car and visually inspect them. Blowing air inside them and checking for air exiting will see if they are plugged. An emissions shop with an exhaust flow sensor is the best place to have the cats checked at. Also, you could put your hands over the exhaust and wait for a few seconds and then release them. If the air blows out strongly then you most likely don't have plugged cats.