After vanquishing the Wight Knight, you must talk to Simona's old nanny in Zere.
Zere is northwest from Loch Storn. You need to find Princess Simona's old nanny, Alanna. During the day, she is visiting Petra's house. Petra lives in the northeast corner of town. You have to go around the town clockwise to get there.
Once you find Alanna and Petra, they will sing the nursery rhyme of the Right Knight for you. The only clue in the song is about going north.
Your next destination is Doomingdale Forest, which is northwest from Zere. Be sure to upgrade your equipment before you go.