If one is not sure if one is a cohen, should his first-born have a pidyan haben? Should he duchan?
1. No pidyon haben, no duchening. 2. What is the source of the doubt? If your family has a tradition of being Cohanim and it is called into question, check with a Rabbi if a real doubt has been raised. OTOH if your family has no such tradition and the question has been raised, you cannot assume you are a Cohen unless there is proof.