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, which is in the northeast corner of town, which you can reach by going clockwise.
Once you find Alanna and Petra, talk to Alanna and 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 Doomingale Forest, which is northwest from Zere. Be sure to visit the Zere item shop to upgrade your equipment before you go.
There will be a cutscene as you exit the town.