There are 1028 known systems with Jove Observatories, but these are player-reported (please get in touch if you find one not on the list).
They're fairly evenly-distributed around KS, varying from ~14 to ~22% coverage. If you want to sort regions by JO count, do so here, at the right of the first table.
Unidentified aka Drifter wormholes spawn in 1024 of these systems (the four JOs in Pochven seem to be inactive).