It's worth noting that not only that, but just a few minutes prior had tried to question Rittenhouse about not telling his story to the media before he got on the stand, and the judge also had to dismiss the jury so he could admonish the prosecutor about that. So this was the 2nd time in like 10 minutes that the judge needed to dismiss the jury to talk about the prosecutor's misconduct, so this time he was really gonna get it.

If you don't understand why asking about his silence on the case is a big no-no, the 5th Amendment states you cannot be compelled in a criminal case to be a witness against yourself. Courts have long held that this protection also means that prosecution cannot use someone's silence as evidence, or use it to imply guilt, or question the defendant about their silence should they choose to testify. This isn't some obscure or new rule, so it's something the prosecutor definitely knew he was violating.