To reach the Ancient Wardstone that starts this quest, go to the Casino (2nd floor) and take the ramp up from the very back, then turn right and follow the ledge and you should see it just below you.
It would seem that there is more than one set of clues you can receive for this quest, probably determined by which Initial Clue you get. When you find each clue the name of the next one will be in the tooltip of the item.
Set #1:
Initial Clue -- on the post next to Dacia Ultan -- 7544, 6380
Caravan Crate - located on a crate in Lantern Hook (SE side) -- 7644, 6386
Ironhook Counterfeit Coins - located on a shelf in the store room of the gambling area in Lantern Hook. It's one level up from Helena and the entrance is directly to her left (your right) -- 7641, 6334
Leaky Bucket - located next to the tree in front of Helena -- 7662, 6273
Set #2:
Initial Clue -- on the post next to Dacia Ultan -- 7544, 6380
Artificer's Hammer - on the bookshelf in the Master Artificer's room ( 7671, 6256 )