Here is a map with all currently known spawn points of the Edge of Reality portal in Spires of Arak.
/way 36.55 18.18 Rocks
It spawns between these two small rocks. Here's a video that shows the person who found it exit the portal.
Thanks to Ritalyn on wowhead, we now also have a picture of the portal, just about to spawn! You can see a dead and decay-like animation on the ground before the portal materializes.
|This is where the portal spawns, near a small wasp critter, between the rocks|
/way 47 20 Lake
Coming from Spires of Arak: /way 50.2 6 Skettis
Coming from Talador: /way 70 84 Skettis
/way 60.8 11.2 Ramp
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.