Well if it's after WWII then I assume that some part of Germany would be taken, 'depopulated' of Germans and offered up as a 'Neo-Israel' (or something like that.
It could be Prussia, Saar, or Bavaria.
If you want a POD before WWII then the Russian Empire could, for whatever reason, take a bit of territory it had taken over and offer it up for Jewish settlement, that could evolve into a Jewish state.
But if you push it back farther, the Khazars (converts to Judaism) could push further into Europe and create a Jewish kingdom in what we know as western Ukraine.
The Germans would never allow them to take the entirety of Prussia or Bavaria. The Saar is possible though.