Recently I have come across the term "Gretchenfrage" so often that I am now taking it up here.
In the book (Faust I), the "Gretchenfrage" is: "Nun sag, wie hast du’s mit der Religion?"
Today the "Gretchenfrage" stands for a question that is asked directly and often abruptly about a content that the questioned person is uncomfortable with revealing. It can be, because her or she does not have an answer or is not very sure of it.
Whenever I have heard it recently, it has mostly referred to the solution of difficult political or climate policy issues.