What exactly is that "jes nes sais quoi"?

Well, I’m at school, and I go into AP English, right? And we have a substitue teacher. She’s very strict, and is one of those teachers that are “over the top” adnd expect the best of you.

So, we had a discussion on Atticus, from To Kill A Mockingbird. She came up to me, because we’ve had her for about two weeks, and she advertised to the whole class that I have the “jes nes se qua” in discussion, and explaining opinions in class. Also, she said I was the best in class, and always smiled when she called on me. Which was frequent. I thanked her for the compliment, but I had no idea what it meant.

I mean, I’ve heard people say it before, but what kind of what are you talking about now?