Gardner Bender line splitters are used for providing a path to share a signal input.
Nothing! A clamp meter will only measure the current flowing through the wire, not the voltage. So a clamp meter will never be able to give you a voltage reading from the clamp section of the meter. You would still have to use your test leads to take a voltage measurement.
As for the current, you need to separate the three wires in the appliance cord. A clamp meter will only give you a reading when you are around a single conductor of the cord. So with the hot and neutral of the cord both inside of the clamp, there will be no reading. With just the hot or just the neutral, you will get a reading.
We do offer an accessory, the E1 Line Splitter, that helps with this. This allows you to plug your appliance in on one side, and plug the other side into your receptacle. From here you can take an exact measurement, one that will be multiplied by 10, and you can use your test probes from your meter to test the voltage going to that appliance through the Volt Check holes in the top of the unit.