You should get yourself familiar with Google Analytics,
or even better if you can try it out in your own websites.
Oversimplified, Google Analytics allows us to track client-side events with easy-to-integrate script tag and then do complex analysis with their dashboard.
For example, you can cover topics like:
- script tag API design
- loading strategy
- performance concerns
- cache control and update strategy
- data protocol
- some basic backend design including load balancing and storage .etc