Des Pudels Kern--question for German speakers

I am doing some research for program notes for Boito’s Mefistofele, and I just discovered, to my delight that in Goethe’s Faust, Mephistopheles first appears as a poodle. This scene is (or was) so well known to literate Germans that it gave rise to the expression “des Pudels Kern,” meaning the true underlying nature of something. I would love to know, is this term still current in Germany? If so, is it esoteric, or something any school child would know, the way, say “to be or not to be” is still generally recognized in America?

Hmmm - i certainly do know it as a saying (independent of Faust) but i can’t recall hearing it for a long time. It seems to have a bit of an old-fashioned vibe, i would be surprised if my students ever used it in daily conversation. The older ones may have heard it (especially since Faust is a standard text for classes) but i don’t think that younger kids (12 and lower) are familiar with the expression at all.

Recognized by educated people; used as much as anyone would use casual allusion to the classics, i.e. rarely even by the educated.

Thank you. I guess that’s about what I expected. (Although I hoped you’d say, Oh yes, everyone knows that.) I’m interested to know students still read Faust in school. This would be the oldest kids, I assume? It seems like pretty demanding fare.