The chest is at 54, 35. It's on a small pedestal.

Ok, so the majority of the comments give coordinates, but if you're like me, you don't know what any of it means. So here is the close to exact (if not exact) guide to finding the wooden key and chest/box.

1st of all, try to be a level 27 if you are going to handle the ancients (who have the key) because sometimes there will be 2 or 3 of them on you at once..

2nd to find the ancients, follow the path that leads to felwood but don't enter felwood. The path towards felwood is a main path on your map that splits north of the main path ( the path toward felwood is located east on your map from Shael'dryn at the moonwell). And it too has moonlight lanterns on it.You know that you are about to enter felwood when you see moonlight lanterns that are green instead of blue. I warn against entering felwood because the beasts are all unknown and will kill you soon upon entering felwood... Either way, right before the green lanterns, to your left from the path maybe 200- 400 ft. from felwood, there will be ancients guarding the box, and they are roaming around near tucked away broken pillars. Kill all the ancients in that spot and retrieve the wooden key from one of them.

3rd there are 3 pillars that are glowing pedestals in a row inside the half circle of broken pillars. one of them has the chest/box casually set on the top of one of them. Right click on the box to open it.

4th and final the iron shaft should appear and you simply take it by clicking on the Iron Shaft that appears.

5th take the moonlit path back to the main moonlit path (go right) and take the moonlit path back to the hidden path back to the person who gave you this quest >(Shael'dryn at the moonwell).

Ok? X) Good luck... I hope you spend less time on this quest than I have and find this little quest guide helpful. X)

Added:
P.S. I would recommend referring to the post by {Raruthga} (that is the 5th post up from mine) if you are confused in anyway about finding the felwood path in my little guide in the second rule there.^ Ok, that should be everything. ^.^

P.S.S. The screen shots for this quest are also helpful, especially the second one with the little arrow cursor on the map that is in the brown area.. X) That's how I began to figure it out. X)