The statements you make as a juror are made under penalty of perjury. If there is any doubt as to how to answer you can always ask to approach the judge privately and discuss the situation. However, if it is now NOT a conviction, then "no" would be a truthful answer. In jury duty, it's better to disclose, even if that is privately to the Court. A prior felony, even if reduced, may be the kind of information that attorneys on both sides want to know.
Answer honestly. He'll surely get booted. It'll mean his schedule won't be burdened by jury duty but it will also mean that the jury won't get the kind of perspective that it might benefit from. Good luck
As previously stated, he should answer honestly, and if either not sure or not comfortable stating or explaining his situation in front of the other prospective jurors, he can ask to approach, and can then answer outside of the presence of the other prospective jurors and, in some cases, only in front of the judge, the attorneys, and the court reporter.