If an FBI agent comes to your home or workplace, you do not have to answer any questions. Tell the agent you want to speak to a lawyer first.
If you are asked to meet with FBI agents for an interview, you have the right to say you do not want to be interviewed. If you agree to an interview, have a lawyer present.
You do not have to answer any questions you feel uncomfortable answering, and can say that you will only answer questions on a specific topic.