hi i need help with the quest curing the poisen, i dont know where to find the earthroot

Try the Auction House, Earthroot is a low level tradeskill item collected with the Herbalism profession.

Have you tried asking in the general or trade channels? It's so cheap that you might find a friendly herbalist who's prepared to hand it over for free, or for a small exchange. When I needed some, I asked and was given some for free, but I gave the guy a healing potion for his trouble. Nowadays, with my herbalist alts I'm repaying the favour by handing out the Earthroot.