Kirka is a herb that is used in Cooking that can only be found around the Sprigg Habitat in Morheim. If you're looking to level your Extract Vitality skill Kirka is the best option for you to raise your skill from 180 to 200. As far as farming specifically for Kirka, it definetly won't be the best income but if you wan't it for some sort of food, go for it.
When farming for Kirka there aren't really any mobs that you'd have to watch out for but this path is very commonly used by Elyos that are Rifting. This of course is something to keep in mind if you hear reports about any Elyos around in the area.