There are already math proofs made by humans on this very day that are hundreds upon hundreds of pages of lemmas that are highly advanced and building on other advanced results. Understanding such a proof is an undertaking that literally takes years. An AI might end up doing it in minutes. But what an AI could cook up in years could take a human... several lifetimes to understand.
As another example, take the design and fabrication of a modern microprocessor. There are so many layers of complexity involved, I would bet that no single person on this planet has all the required knowledge end-to-end needed to manufacture it.
As soon as the complexity of an AI's knowledge reaches a certain point, it essentially becomes unteachable in any reasonable amount of time. Perhaps smaller sub-parts could be distilled and taught, but I think it's naive to assume all knowledge is able to be sliced and diced to human-bite-sized chunks.