This works the same as the original, once you get to the Scrollroads past the desert area, if you follow the path West from the save statue there is a guy who will give you From Beyond Talent that you need to equip. Whomever you are playing as in the map needs to have this on to see the ghosts. For example, if your collecting flowers with Gnart and want to kill you some ghosts, he needs to have the talent equip. I've noticed they also need to be in your battle group, correct me if I'm wrong on that one.
Once you have the talent on you can see them as you would any other enemy. The only exception is that they are a one time only mob, meaning if you kill all of them in the Scrollroads, they do not respawn.
Best way to get this quick: teleport back to Ramoo, then work your back to the desert. You find them in groups of 2 to 3, and they are everywhere. They are also scaled to the area you find them in, so basically the ones in Ramoo are a lot weaker than the ones in the scrollroads, who are weaker than the ones in Nadir ect.
Hope it helps!