Arvak's Skull in Dawnguard (The Elder Scrolls 5: Skyrim)

at the very end on the right (if you look at the palace where the vampire sits), look on the right side. More precisely, I can not say there and so the hell will you understand where? what?

If you see ghosts standing around, you go there.

Thank you guys, I found it.
Perhaps I'll post screenshots

here he is

and what gave? if it's not a secret, otherwise I found a horse, but his skull is not ...

no where did you find the horse

People, I cannot complete the quest with him, writes: "find the skull of an arvak", I found it a long time ago and gave it to the owner, but the quest itself remained hanging, and when shown on the map, it leads to the cairn of the holder, how to remove the quest?

201Distoact0
If you gave it away and the quest was not completed, then
setstage DLC01SoulCairnHorseQuest2 255
If you read any stage, then first 150, and then 255.
But keep in mind that Arvak's call may not appear.