I don’t very understand which server you want to monitor.
If you want the CPU usage of the Web application’s server, you can click Add Computer in Manage Counter Sets to add the computer where the server is located on to monitor. In addition, you must add the computer to the Performance Monitor Users group in your
test controller. Then you can know the CPU usage of the server by the %Processor Time Counter.
The link below about how to manage counter sets using the Load Test Editor may help you:
If you want to know the CPU usage of four test agents where your test runs, every agent’s CPU usage will be displayed under the Controller and Agents in the load test results. You can analyze the %Processor Time to get it.