Talk to Colleagues
As a starting point for finding out what prior knowledge students bring to your course, talk to colleagues who teach prerequisite courses or ask to see their syllabi and assignments. This can give you a quick sense of what material is addressed, and in what depth. It can inform you to differences in approach, emphasis, terminology, and help you address potential gaps or discrepancies.
Ambrose, S.A., Bridges, M.W., DiPietro, M., Lovett,M.C., & Norman, M.K. (2010). How learning works: Seven research-based principles for smart teaching. San Francisco, CA: Jossey-Bass.