If you are monitoring a 120v circuit, you use only one CT. Leave the other one closed but with nothing running through the loop. If you are monitoring a 220 circuit, you need to put one CT around each of the hot wires, usually black and red. The red dots should both be facing the same way, by convention the dots should be from the source of the power, away from the appliance, but it really doesn't matter for a simple monitor of one appliance.
If this is not clear, a little more description of your application will help get you the advice you need.