This page in our guide to Greedfall contains a walkthrough for the On the High King's Trail quest.
You can now meet and talk to any clan leader - Dierdre, Ulan or Dunncas. Ask them about Constantin's disappearance (some clan leaders may not want to talk to you if you haven't helped them in the past). You have been assigned to question relatives of the High King in Wenshavarr. Once you do that, you'll be ordered to find and talk to Cera. It turns out that the woman is trapped and you have to free her.
You have two options - you can rush into the thick of the battle and carve your way to the woman, or wait for the night and get to Cera unnoticed. Whatever your choice, go with the woman to the cave of knowledge. Walk around the other rooms of the cave, looking at the pictures on the walls. Eventually, Cera will leave you, and you will have to leave the cave on your own - choose an alternative exit and follow the woman.
It's time for a long walk - you have to watch out for traps set by the women, but after a while, you will find a passage in the mountains. Proceed and you will find a path leading to Vinbarr's Sanctuary. Complete the quest and you will get 2000 XP. You'll also start the quest Vinbarr's Sanctuary.