One option is to turn on Telemetry Logging of engine and check the generated log. Knowledge Article below. The log is not very user intuitive though, it may be helpful to find out what is resource intense.
There are two discrete elements to this question: (1) what is the server level usage, (2) what are contributing to that server level usage.
For (1), you can use the Performance sheet on the Operations Monitor. This app is bundled with Qlik Sense. It visually displays high level performance metrics over time. For example of a work-flow that is unlocked, you can:
Drill into time periods where CPU utilization over the interval (5min) was over 80%
With the time periods narrowed, you can navigate to one of the Session related sheets and figure out which apps were open during that time period