Contract: Jenny o' the Woods - Velen
Quest Giver: Midcopse Notice Board
Other Requirements: N/A
You'll receive this quest be investigating the Midcopse Notice Board at any point after arriving in Velen. After you do this you'll need to speak with Ealdorman Bolko who will update your quest and tell you to speak to a few other townsfolk. All of them will be marked on your map/compass so you'll have no issues finding them.
Speak with everyone marked on your compass in Midcopse to advance the quest forward and receive a new quest marker to the north. In the fields to the north of Midcopse you'll have to investigate some torn clothing and footprints while using your Witcher Senses.
Follow the foot prints a short distance northwest and you'll find the Murderer's Knife a letter as well as the place he buried the body. Your quest will update and send you back to the Ealdorman for more information about the women. Speaking with him will update your quest for the final time and lead you to the area where you fight the nightwraith.
Meditate at the camp site if you have to until 9pm which is the earliest that Jenny will come out to play. This fight is very similar to the Noonwraith fight in White Orchard, you'll want to drop a Yrden on the ground to make the wraith vulnerable to your Silver Sword then beat on her as long as she stays in the circle.
Jenny's special ability is sometimes she will despawn and make 3 regular nightwraiths attack you. During this period she will regenerate her health so it's important you take out the nightwraiths that she spawns as quickly as possible.
Jenny o' the Woods Weaknesses: Specter Oil, Moon Dust and Yrden
Once Jenny o' the Woods is defeated you'll want to return to Ealdorman Bolko and speak with him to complete the quest and receive your reward.