Envoy to the Elves is found on the Main Map. When you are in the quest map, simply press the backward circular arrow to access the main map. From there, it is located on the first main map page you started from that has The Cliffs and Baron Castle quests on it. In other words, it is the map on the top left quadrant of the main map. In that quadrant, it is located just southwest of Baron's Castle. The Envoy to the Elves quest can only be found on the main map and uses 10 Energy to do the quest. Also, it may be good to add that if you are doing this quest in the hope of getting Nightshade for alchemy recipes, you may have to do the quest more than once to get it. Other rewards include Ginseng.
Another place is south of Baron's Castle in Forage Forest doing the task Forage for Ginseng (12 Energy).