Originally posted by carver9
Prove that his claws are made of different substance than the bone Superman broke.
There's no need for me to prove anything; the burden is on you to show that they are the same. However, I'll provide some relevant points:
1. Not all bones are equally durable in animals on Earth. By extension, under the suspension of disbelief, it's reasonable to assume that the bones of an alien species may vary in durability as well.
2. Hardness is just one factor in the ability to cause damage. Sharpness is another. It's possible that Doomsday's claws are sharper than the bones protruding from his face. That's also assuming the angle of attack was the same in both instances. In other words, It's possible that Superman struck the bones on Doomsday's face from a less optimal angle, such as from the side, where the impact wouldn't be as sharp.
3. Doomsday cut through flesh that wasn't reinforced by bone. Superman's fist, on the other hand, is reinforced by bone, which makes it significantly more durable than the soft tissue Doomsday sliced through.