Gretchenfrage

Etymology
Compound of Gretchen (diminutive of the given name Margarete) and Frage "question". In reference to Goethe's Faust (published 1808), where the character of Gretchen asks the protagonist, who is secretly in league with a devil, wie hast du's mit der Religion? "how do you feel about religion?". The expression is of mid-19th-century coinage (attested 1865 in Löwe (ed.), Schlesische Provinzialblätter issue 1168, p. 147).

Noun

 * 1) a question as to the addressee's religiosity or belief in God
 * 2) any question going directly to the core of an issue
 * 3) a crucial question that usually has a difficult or unpleasant answer