Can anyone point me to where it is ? The wiki says https://wiki.guildwars2.com/wiki/Riddle_of_the_Scourge which is not helpful at all. A game link to the location would be very nice.
Do what it says, Explore Salt flats with your Jackal. So you should be looking for sand portals with that clue (you need to have the Mastery to use the portals). The sand portals and sand walk lead you to the Runeforgers Chest.
“each chest contains a certain exotic ring needed for each Ascended Specialization weapon collection.”
The above was written as part of an attempt to waste time.
For a little more guidance - near the mastery symbol over Salt Flats, head NW and look for sand portals, one will take you up on a mountain peak, where there is another portal. Follow it.
I also recomend doing this at night - the visuals there is absolutely stunning then!