Legal Question in Civil Litigation in California

Generally, you have a right to a witness fee plus mileage. If you are an expert being asked to testify as to your expert opinion, you have a right to be compensated for your time at a reasonable rate (or your regular rate). You have your constitutional rights, including the right to privacy. You have the right to retain your own attorney. It's hard to say what else might apply without more facts, but if you believe you are being wrongly compelled to appear, you may be able to bring a motion to "quash" the subpoena, so you do not have to testify.