I've done a variation of this exercise with some folks I helped to interview.

We showed them our website and asked how they'd investigate/troubleshoot a complaint that the site was "slow."

Then we kind of role-played the troubleshooting process. Ideally I wanted them to determine if the site was slow for everybody, vs. just the person that reported the issue. If it was only slow for a single person, was it their account, or many just their internet connection? How would they determine that? If we determined the issue was happening for everybody, how would you determine which part of the stack was slow? Etc.