top should show a real time list of running processes sorted by their CPU consumption. Since it's updating every second or so, you may see the list jump around a little bit. Here is an output from one of my Pis with Cayenne (and nothing else of note) running:
The Cayenne Pi agent is the python3 entry. In my case its bouncing between 10% and 30% CPU which seems pretty normal, isn't causing any performance issues. If you kill it though, Cayenne won't be able to interact with your Pi or see it as online until its running again. Easiest way to do that is just reboot the Pi and it will start at boot time.
If it's consistently pegging your CPU after each reboot, until we make any improvements to the agent performance, you could connect the Pi via the MQTT API instead. In that case there would be no agent software running on your Pi, and sensor/actuator data would be controlled by MQTT functions instead which I assume will be much lighter weight.