The fastest way to reach Shar'thos is by using the flight master and fly to Garden of the Moon. From there you should mount up and ride north. The part going north will directly hit his spawn area, and you will be notified by the World Quest marker when you are within range.
Loot from Shar'thosShar'thos can drop ilvl 680 chest pieces, as well as a shadow relic, a cloak and a trinket. These can all be rolled by killing him, and by using a Seal of Broken Fate for a bonus roll. You will only recieve loot on the first kill each week.
In addition to regular loot, he also drops Skull of Shar'thos, which is part of the Fury Warrior Hidden Artifact Appearance. This has a 100 % drop chance is you are exalted with the Valarjar, and a lower chance if you are revered.
If you want this skin for your fury weapon, I recommend to gain as much Valarjar rep before the week is over, and hopefully you will hit exalted before he despawns. Due to the number of World Bosses, it might be 11 weeks before he spawns again. We recommend reading out Valarjar reputation guide in order to maximize your rep gains before he despawns.