You’re just pretending to be dense, aren’t you? I said find a case that otherwise doesn’t run afoul of Constitutional principles, such principles definitely including the Equal Protection clause of the 14th Amendment. Find a case where the opinion says the law is ruled unconstitutional solely because it was motivated by partisan bias even though it was otherwise Constitutional. Once you said that gerrymandering ran afoul of the Equal Protection clause, the fact that it was motivated by partisan bias or not became irrelevant.
The census question does not appear to violate the Equal Protection clause. What Constitutional principle does it violate? Until you can answer that, you could say the Devil himself thought up the idea and it would still pass Constitutional muster.