Your question is Design a Recommendation System. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Design a recommendation system (with many side questions probing depth on each topic).
Asked in the ML system design stage. Explain how you would clarify requirements, size the system, choose retrieval and ranking approaches, design online and batch serving, and evaluate the system. Discuss feature freshness, training-serving skew, monitoring, experimentation, and failure handling.