Legal Question in Criminal Law in California

If you were properly served with a subpoena, you must show up to court. From there, the only way to avoid answering questions is if there is a privilege (such as the Fifth Amendment privilege against self-incrimination) that would allow you not to answer questions.

If you showed up, but refused to answer questions, you could be held in contempt of court.

If there is something more substantial to your question, and depending on what the underlying case is about, you should voice your concerns either to an attorney you consult with or the attorney that subpoenaed you.