Treating Zwerk is an optional objective of the main questline: The Finger of God in the Kingdom Come Deliverance 2.
Out of 26 total objectives in the main questline, 11 are optional, including treating Zwerk.
The main quest, The Finger of God, starts after Father Godwin tends to Captain Jan’s wounds. As Henry of Skalitz, you should accompany Father Godwin to perform rites for the fallen and help the wounded.
Treating and helping the wounded allies is essential for future fights. So, before you rest for the night, try to treat as many allies as possible, as their recovery will determine their usefulness in combat. However, you need a decent level of Alchemy and Craftsmanship to do so.
Find The Wounded In Lower Castle And Treat Them
So, before you put your Alchemy skills to the test, you should talk to Klara to learn the names and locations of the wounded men.
She will provide information about three wounded men, Mark, Zwerk, and Kozliek, resting in the Lower Castle.
However, before you head to the Lower Castle, be sure to take the potions, bandages, and schnapps from Klara’s cabin just below the smithy.

The supplies, i.e., Embrocation, Weak Chamomile Brew, Weak Painkiller Brew, and Schnapps, will be in the chest up the ladder of the cabin.
Now that you have collected the supplies, head to the Lower Castle to treat wounded men. Remember, success depends on both correct choices and skill checks. If you have low levels of skill required, it will fail.
Treat Kozliek
When you arrive at the Lower Castle, you will first notice wounded and sleeping Kozliek. Approach and examine him. Remember that your choices add to your Survival, Thievery, Craftsmanship, and Alchemy.
Use the supplies from Klara’s cabin here to treat Kozliek. Give him Fever Tonicum, a potion for fever, clean his wounds with Schnapps, and change the bandage to wrap up the treatment.
Treat Mark
After treating Kozliek, lying right next to him is Mark. Examine him and give him a Painkiller Brew to ease his pain, clean the wound with Schnapps, and dress the wound to help him.
After successfully treating Mark, you should see an objective complete check mark.
Treat Zwerk
And finally, go downstairs to find Zwerk. It will be dark down there, so pick up a torch and find Zwerk. But remember, you’ll need four servings of alcohol.
If you don’t have it, there is a chest in the corner with a medium lock with 2X moonshine that includes other useful materials like Hare Pelt and Roe Deer Hide.
Examine him and give him Drinking Water, rub his ankle with Chamomile Brew, and clean his would with Schnapps. To finish the treatment, wrap the wounds with bandages.

Once you’ve successfully treated the wounded, step outside to talk to Klara, and she will reward you with a Strong Painkiller Brew, Strong Artemisia, Bandage, and Strong Marigold Decoction.
Now, if you want to be involved in a romantic endeavor with Klara, choose the dialogue option, “Let’s go and get that drink”—you’ll need 15 Speeches to succeed.