However, there may be other passages in W's writing that directly relate to what it means to understand something. I can't recall off the top of my head these passages but I did write one comment regarding some at least W inspired thoughts on what it means to "understand".
There are probably more relevant Wittgenstein passages in the PI or other of his works regarding what it means to "understand" something. Is it simply the ability to explain some concept with precision? Well, physicists can certainly do that with mathematical precision! So there's some other element(s) one may reason. Perhaps that other element is something like a loss of a "weird" feeling. So because experts and laymen alike still have this weird feeling when thinking about the nature of quantum phenomenon, we say that we don't completely understand it. But perhaps this recalcitrant weird feeling we have is simply a cultural relic, something that is a result of cultural (or socio-linguistic) biases.
It would be interesting to test this out. Maybe people from other cultures, cultures that are perhaps more comfortable with things like ambiguity, vagueness, indeteterminancy, etc, such as many Asian cultures will not have this bias and see quantum mechanics as "natural" and will say that they fully understand it once they understand the mathematical descriptions.
This understanding of understanding as it related to quantum mechanics s what I think W will endorse.
When a physicist or Robert Wright says he doesn't "understand" the nature of Higgs bosons or that it "make no sense" could it be that they only "understand" something maybe W's remarks on rule following will shed some light? One interpretation of W's ideas on rule following is that there has to be a further element other than rule following itself, that is, besides the applied ability to follow that rule to understanding rules of language. On some interpretations of W's remarks, that void is a social element. The social element, as far as I can tell, has to do with social expectations of what other people expect. So it's not enough to follow some rule (formal mathematical or informal linguistic rule e.g.) but there needs to be some expectation that society will accept your explanation of your rule following. In our culture, since quantum mechanics is so counter intuitive to so many, it may just be this element of a lack of social acceptance that is the missing piece to truly understanding quantum mechanics. But notice that this is a cultural bias contingent on the culture and times we live in. Maybe as more of society come to accept quantum mechanics, it will seem less weird and hence, at least according to this interpretation, people will be less likely to say that they don't "really understand" quantum mechanics?