Welcome to your interview.
The question is on your right: Privacy-Preserving Recommendation Engine. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
If a client asks you to build a recommendation engine but has strict data privacy constraints, what approaches would you propose?