In Wolf's Clothing - Skellige
This quest is automatically given to you while doing the Nameless Story Quest and many of the first objectives for this quest will be completed during the course of the Nameless quest as well. The first few objectives of this quest, involving finding the garden and speaking to Josta and Melitele are all completed while doing Nameless.
For this quest the first objective that branches off from Nameless involves finding Morkvarg. Just north of where you find the levers for the Nameless quest there will be a cave where Morgvark resides (pictured above) speaking to him in here is required for this quest as you'll learn much more about what plagues him.
Each time you encounter Morgvark and beat him up you'll have some dialogue where you can either feed him, finish him off, leave him alone or ask questions. Any food you feed to him turns to ash, feeding Morgvark's own flesh to him will kill him and fail/complete the quest. It's recommended that you don't go this route as there is an additional reward for you if you complete it properly.
Tip: Choosing "finish him off" during the dialogue options while talking to Morgvark will allow you to loot his corpse. He drops a Werewolf Mutagen and since Morgvark always respawns until you complete this quest - you can effectively keep doing this and farm the Mutagen from him.
The next thing you will have to do is find the Padlock Key that Morgvark told you about when you faught him in his cave (pictured above). To reach this key you will need to open the right sluice gate and swim under the waterfall to find a secret cave. For more information how the levers and the sluice gates work I highly recommend you read the Nameless Quest Walkthrough. I go into much more detail there.
Once you've obtained this key you'll want to use it to open the door on the building in the center of the garden. In here you will find some crafting recipes as well as Morgvark's journal that you'll want to wait to read. There is one more quest marker we've been neglecting outside of the garden, a man named Einar in the town of Larvik to the southeast.
Speak with Einar in Larvik and he will tell you a story about Morgvark. Read the journal and your quest will update, suggesting you ask Einar why he is lying. If you read the journal prior to speaking to Einar, just select the dialogue option "Lied to me" whenever it appears for you.
Depending on the options you choose with Einar you'll either fight him and have to loot the necklace from his corpse or he'll give you the necklace when you tell him you want to lift the curse. Note: If you don't learn about the curse from Einar before killing him then the only way to lift the curse from Morgvark will be feeding him his own flesh, thus getting you the worst outcome of this quest. It's best to let Einar live and have him willingly give you the necklace.
Return to Morgvark and either feed him the werewolf flesh that you loot from his corpse after choosing the dialogue option "Finish him off" or give him the Cursed Fang talisman to lift his curse and free him. If you lift the curse from Morgvark you will be able to go to the Loan Shark in Novigrad and claim an additional reward from him. Otherwise you'll just have to return to Josta and claim the reward from her.
Tip: Freeing Morvgark properly also gives you credit towards "helping Monsters" for the Contract: Skellige's Most Wanted Quest.