This is one of the most important moments. Answering it poorly can cost you tens of thousands of dollars. The goal is to avoid anchoring while remaining professional.
Best response: "I am more focused on finding the right role and team. I am confident we can reach a number that works for both sides once we determine there is a mutual fit. Can you share the total comp range for this level?"
If they insist: Give a wide range based on market data. "Based on my research, Senior PMs at employers of your stage and scale earn $300K-$450K in total comp. I would expect something in that range."
If asked about current salary: Note that California, New York, Colorado, and several other states prohibit employers from asking about salary history. In other states, share total compensation (not just base): "My current total comp including equity and bonus is approximately $X."