First, there are two Skahyir's:
One is a quest spawned dragon for the Arios 55 quest in Pasha's chamber in Box Canyon (map)(NE). This mob will only spawn if it is in your quest log, and your log says to see Pasha. This dragon is the easiest of the two and can be solo'ed if you can survive his breath crit. Use LR to resist.
To find the random spawn Skahyir, run North from Oasis till you get to box canyon, go west around the mtn, throught the arch and then follow it north/east all the way to a cave with two inferno drakes guarding it. Enter the cave, Ska spawns at the bottom, on the pile of gold. Skahyir is not a triggered spawn, and will require camping (Bordeal said Skahyir has an average spawn rate of 3 days. That translates into a 1% chance of spawning per hour, GL). Use LR for resists, this mob is considerably tougher but can easily be killed by a group of 55+.
This mob drops the Crown of Ragnet, needed for the Plane of Sky portal quest.