The interviewer says "Design a dashboard for viewing analytics." What is the best first move?

The best first move is to ask who uses it, which devices, how fresh the data must be and how much data a chart shows. These answers decide almost everything else. For example, they decide polling (the client asks again and again) versus push (the server sends updates). They also decide whether charts need downsampling, which means showing fewer points than the raw data has. "Start sketching the component tree" is the tempting wrong answer. It feels productive, but you risk designing the wrong thing.