Nameless - Skellige
This quest automatically begins after the Missing Persons quest is completed. Nameless is the second quest in a chain which concludes with The Calm Before the Storm. You'll also receive the quest In Wolf's Clothing, which is a secondary quest and goes hand in hand with Nameless.
For the start of this quest follow Yennefer to the large tree where there will be some dialogue and she will let you go on by yourself. All you have to do is follow the werewolf foot prints now; the rest of the evidence isn't required to advance the quest forward.
The foot prints will lead you clockwise around the area until you reach a locked door, which is where the blood trail ends. Use the wall nearby to climb up and head over to the other side of the compound, where you first started following the foot prints. Run past the shack and across the wooden bridge - there will be a bunch of foot prints in this area that glow red using your Witcher Senses.
In this area you will also find a wall that you can climb up and a Lever which will operate the sluice gate for you. I've provided a screen shot of this wall below so you know what I am talking about, it looks like a normal wall for the most part but you can climb it like a ladder.
North of the levers (as shown on the map above) you'll find a cave entrance. Inside of that cave you'll find Morkvarg and receive credit for the Secondary Quest, In Wolf's Clothing. You should do this before progressing any further ahead in the garden.
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 the In Wolf's Clothing quest - you can effectively keep doing this and farm the Mutagen from him.
For those of you having trouble finding where this lever is, use my map above for some better guidance. Where you see me standing in the screen shot is where you'll find the concrete wall to climb. Now, let's explain the lever mechanism (pictured below).
On either side of the wooden machine pictured below you'll find two levers. The wooden peg in the middle of the machine that you see sticking up tells you which gate is currently selected. You use the right lever to change which gate/wooden peg is selected and you use the left lever to open or close that gate.
You should open the right most gate first so that you can collect the quest items in there; you'll have to swim under the waterfall near the second gate to find a secret cave that leads to these quest items. After the right gate take the middle one for the main quest.
Here is a quicklist of what you will find in each of the three areas after opening the gates:
Right Sluice: Padlock Key (Quest item), Chest & Info about werewolf
Middle Sluice: Meet Morgvark/Continue Nameless Quest
Left Sluice: Exit the garden
Going through the middle sluice will let you into the part of the garden that was previously locked off. In here you will want to investigate the house Morgvark was being held in for another cutscene with 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. There is nothing more you can do unless you progress the In Wolf's Clothing Side Quest further.
When you're ready to progress the Nameless quest further you'll have to jump down into the well, the location will be marked on your compass/map. Upon discovering a body in the well this quest will conclude and the next one in the chain, The Calm Before The Storm will begin.