Skeleton spawner has been turned into a very simple trap dropping skeletons into a hole, where at the bottom tamed wolves can attack them for XP/loot. as of 19w08b the wolves no longer track or attack the skeletons from the spawner. taking them out into a field at night though they do attack naturally spawned skeletons.

I expect the change in behaviour is likely somehow due to the skeletons not being able to see me the player, but possibly because of the different spawn mechanic. (I recall hearing something about mobs and tracking through blocks changed recently, this could be a side effect)

Expected behaviour is Wolves attack the skeletons. This is a long standing design that has worked as far back as 1.8 for sure.

Might be related loosely to https://bugs.mojang.com/browse/MC-144763