Here is a map with all currently known spawn points of the Edge of Reality portal in Frostfire Ridge.
This screenshot from a user shows a spot where you can keep watch on all 3 known portal spawns:
|All 3 portal spawn points|
/ way 51 19.8 Ramp (bird)
/ way 52.5 17.8 Rylak
/ way 53.8 17.3 Trees
/ way 47.7 27.5 Harrison Jones Daily
|By Enumatse, Wowhead|
I was fortunate enough to have stumbled upon the portal without needing to camp for it. I was just doing the Harrison Jones daily (The Blessing of Beasts chain) when I caught sight of a portal out of the corner of my eye. It spawned at about 47,27 in Frostfire Ridge, down the little raised section of rock where the altar to lure the Rylak is. It spawned near the two large, dark spires jutting out from the mountain, right in the little gap between them.
I didn't write down the names of the people who took the screenshots, but feel free to let me know if you want your name added etc. I will also do my best to add names when I find them again. All the ingame pictures are from wowhead.