How do you format punctuation marks around a title that already has punctuation marks? [duplicate]
According to the proscriptive rules of English grammar as presented by the Purdue Online Writing Lab, you should place punctuation such as questions marks after quotations (i.e. outside the quotation marks) if, for example, the question mark applies to the sentence as a whole. I can’t see any reason why that would change if the quotation ends in a question mark.
So your example ‘What does Carl Sagan assert with his example about table salt in "Can We Know The Universe?"?’ is correct.
I agree that the ‘?”?’ looks extremely awkward and I think the best solution would be to reformat the sentence to something like
In his example about table salt in “Can we Know the Universe?”, what does Carl Sagan assert?.
Also as you can see I don’t follow a number of the “rules” made up and promulgated by grammarians; many of them are arbitrary and contrary to actual language use in various dialects of English, so (please excuse the pun) take this all with a grain of salt.