Your question is Design an Open-Ended ML 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 an open-ended ML system in the ranking/recommendation/prediction space (candidate compared it to designing an email spam filter), choosing your own features and metrics.
Asked in the ML design (L4) stage. The candidate picked the direction, and Google let them guide the discussion. It was described as easy, with no quiz-style trivia.
Explain your assumptions before designing the system. Cover the complete lifecycle from data collection and labeling through modeling, serving, evaluation, and monitoring.