I'm on my 5th week of clinics now (3 services so far), so still really new, but...
My advice: You may not know anything about a topic, but imo a clinician is more likely to appreciate you trying/guessing intelligently rather than just averting your gaze and staying silent. You may feel like an idiot (I definitely do), but you'll be surprised how often the answer you're thinking in your head will actually be correct, or at least on the right path.
Also, prepping for cases the night before really goes a long way.