It demands on what he is asked to testfy about. For example, if he were required to testify about his citizenship, he would be compelled to answer. However, if he were asked to testify about matters that could be considered national security matters, the answer is most likely no. The exception would be if the courtroom were closed to the public and ONLY the Judge, Prosecutor, Defending Atorney and (maybe) the Jury could be present.
Once everything comes unsealed it ALL can be used as evidence of something and that even includes his school records if he was claiming to be a foreign student.
Claiming to be a foreign student alone would be a felony and enough to impose heavy punishment but even greater are the penalties if he obtained the office of president while he was never a ‘Natural Born’ or even a ‘normal born’ citizen.
The roof and more MUST fall on this traitor who is actively trying to overthrow the U.S. government and constitution.