Well that looks like the outer skin on the transom and it is cracked because you tried to separate the wood from the skin using some sort of prying effort. And the wood won that one. However, remove the wood by grinding and such and you will deal with that crack when replacing the transom back again. Ground the outer skin so you can use polyester resin and cloth to repair it. but after the wood transom is replaced first. When installing the actual transom wood covered in polyester and CSM as you can see and read about with so many others in these forums, use a piece of plywood to clamp on the outside of the transom to make certain the new wood being installed it totally flat again. Then after that cures, you can work the outside. This is just my opinion and other will chime in with their ideas...