I read it as knowing it at all but maybe it’s the mathematical shorthand subset.

The notebooks were transcribed to regular German by a couple[0] who learned Gabelsberger just for that purpose. There is a bunch of analysis of them in Gödel's 5-volume Collected Works. I'm surprised if there was any interesting mathematical content left to be found. The question that mathematicians wondered about the most was whether he made any progress on the independence of the continuum hypothesis (later proved by Cohen). It appeared that he had some thoughts about it but didn't get anywhere. The question the public wondered about the most was the supposed loophole he found in the US Constitution, but they didn't find anything about that.[1]

There's a cool suspense novel "The God Proof" about finding a lost Gödel notebook extending Gödel's ontological "proof" of the existence of God.[2]

0. John Dawson and his wife whose name I've forgotten. John Dawson later wrote the Gödel biography "Logical Dilemmas".

1. https://en.wikipedia.org/wiki/G%C3%B6del%27s_loophole

2. https://jeffreykegler.github.io/personal/gp/God_Proof.pdf