To feed Morkvarg in The Witcher 3, Geralt will need to give him his own flesh, which is Werewolf Meat. However, before feeding him, Geralt will need to defeat or kill him so that he drops the piece of flesh. Once Geralt has the Werewolf Meat, he can interact with Morkvarg and feed it to him to kill him and remove the curse. Its important to note that feeding Morkvarg regular food will only torture him, and the curse prevents him from permanent death.