Wolves and dogs attack skeæetons only if skeleton and dog look each other in the eye. If skeleton cannot see dog, dog will not attack skeleton.
To reproduce, spawn in a wolf, tame it to become dog.
Make a cage with 1x1 hole on top and one block free space on bottom, to allow dog to attack. Spawn a skeleton into the cage, so its legs are free but it cannot see.
Expected: Dog attacks skeleton legs.
Observed: Dog remains passive.
Remove cage and observe that dog now attacks.
Comparable to tracker no. 148047 on Java.
Thank you for your report! Unfortunately, we have to consider this report Invalid.
This behavior is the same as in Java Edition, which started behaving this way a couple of years ago. MC-148047 asked Mojang to revert the Java behavior, but there's no indication whether they intend to do so and we can't assume that they will. It's entirely possible that the Java change was intended to bring Java into parity with Bedrock, in which case changing Bedrock as requested here would break parity between them.
If they actually do revert the Java behavior, then that would be the right time to submit this bug report, because then a parity issue would exist. As of right now, though, there's no parity issue and as far as I know, Bedrock has always behaved this way, so there's no basis for calling this a bug.