During the plaintiffs deposition, at his lawyers office, the defendant was present with his attorney, who was conducting the deposition. In civil court trial, can that defendant be compelled to testify as to what he heard at that deposition?

I'm confused. Why would someone ask the defendant to testify about the deposition when the deposition is a matter of court record?

Can you flesh this out by explaining why you ask and what questions you think the defendant would be asked?

Also, not that I moved this from Small Claims forum since small claims cases rarely involve depositions.

No, a defendant can not be made to testify at all.
Ask your attorney, that is why you have one.

Next the other person is doing this under oath and being recorded, so what is being said, is just read into record.

I sit in on depositions all the time to compare statements with later statements. The depositions are sworn. No one needs to testify as to what he/she "heard" at a deposition.

What is the situation?

As Judy said, the depositions are sworn statements. They can be called into evidence. There is no reason for a defendant to testify as to what he/she "heard" at the deposition.

The only question I would have is what defendant would testify about. The testimony taken at the deposition would have been recorded, and thus defendant would not need to testify about what was said at the deposition. Was there something said or done "off record" that is relevant?