How do you perform wudhu and ghusl over a wound that cannot get wet?

You will perform jabira wudhu. If the use of water is harmful for it, you should wash the parts around the wound from above downwards, in the usual manner of Wudhu. And it is better to pass a wet hand on it, if it is not harmful to do so. Therefore, you should place a clean and pure piece of cloth on it and pass a wet hand over that cloth.