You could trim the knobs-- CAREFULLY-- a tiny bit with an exacto knife or a sharp, strong pair of scissors. Or you could get a hand file, which is more work but easier to avoid overdoing it.
This assumes it really is a tiny rub. For any significant rubbing, you need to replace the tire. I think I mentioned earlier this is no problem with a Bontrager. Take it back, full refund or exchange. Do this before modifying it!
