This herb is probably on of the most unique plant in Legion. Upon collecting the herb you have a chance to summon a Frenzied Fox that will run around dropping more Foxflower. From that point all you need to do is walk over them to collect. However, this herb only spawns in Highmountain. Have a look at the map below for the route to farm Foxflower

 Map of Where to farm Foxflower in Highmountain

Hope this guide helped you with where to farm Foxflower in wow. Happy farming!