If I were asked that question, I think I'd answer it well. Not because I would be able to figure it out quickly under pressure, but because this brainteaser is very old.
When I was a kid in the 1950s I read both it and the original intended correct answer (the North Pole) in a book of brainteasers.
When I got into high school, someone who was actually smart discovered that the answer wasn't unique and that there was an infinite family of additional answers all involving points close to the South Pole, and I read about that, too. I'm not sure where; I think it was in Martin Gardner's "Mathematical Games" column in Scientific American.
There must be million of people who know the answer, not because they figured it out by themselves, but because they read or heard the answer somewhere.
Of all the candidates who give Mr. Musk the correct answer, I imagine very few of them are solving it on the spot. I wonder how many of the others are honest enough to volunteer the information that they had already read the answer.
Or perhaps that's the point--perhaps it's an honesty test rather than a brain-teaser.