iPhoneSimulator.app used to have the ability to show an external display / CarPlay display, but this feature does not appear to be available in DeviceHub.app, making it difficult (/impossible :( ) to test CarPlay features from the simulator.
DeviceHub lacks any CarPlay simulator
Recommended
In Device Hub we do not support CarPlay with simulators. However, Device Hub does support CarPlay for physical devices that are connected with a USB cable. If you'd like to see support for simulators, please file a feedback report (and post the feedback ID here).