Board Thread:General Discussion/@comment-24170171-20180103162457/@comment-27082610-20180104003359

Jaune's  Semblance  was first seen in " Forever Fall, Pt.2 ". [2]  When Cardin attempted to punch him, he visibly winces while Jaune remains unscathed and surprised by the turn of events.

Based on what was shown in there it's most likely a reflective shield.