The 
Yackers'n'Fash side quest becomes available after completing the 
Speak of the Devil main quest (Speak of the Devil guide).
It is the starting quest for the Striped Tonies questline and it centers on a rivalry between two mining groups in 
Kuttenberg: the Striped Tonies and the All Saints.
Tragedy in Danemark is a highly missable task you can start alongside the last section of Yackers'n'Fash at Danemark Mill.
How to start Yackers'n'Fash
To begin the quest, you need to find Foreman Vlach. While he works in the mining area southwest of the city walls during the day, he will not talk to you while on the job.
Instead, head to the Black Horse Tavern in the western part of Kuttenberg between 18:00 and midnight. Vlach will usually be there and will call you over for a chat. He explains that his group's standard has been stolen and he suspects the All Saints group is behind it.
Yackers'n'Fash location on map:
Infiltrate the Saints' Den
Your first objective is to reach the underground base where the All Saints miners congregate. While you can try to lockpick your way through various shops in the city, these usually feature very hard locks. The easiest and most legal way to enter the tunnels is through the Kuttenberg Underground entrance located south of the city walls, right next to the river.
This is the same path as The German's Treasure. You can time both together; see The German's Treasure guide for full detail.
Easiest Kuttenberg Underground route
Start at this close, unguarded entrance:
Then follow the route marked on the map, or the steps below.
Once inside the tunnel, follow the path straight (skip the first left) until you cannot proceed because of a barricade. The only path goes to the left.
You will soon reach the 
Wasteyard interesting site. You can loot it for 100+ Groschen, then continue straight to another interesting site, Underground Crossroads.
Climb the ladder up, then proceed directly straight to find a locked door. Unlock it to enter the All Saints Tavern basement, where the Saints led by Joerg Preng reside.
Negotiating with Joerg Preng
Immediately after entering, the miners will notice you and alert Joerg, which forces you into a dialogue with him.
When you confront Joerg, you have several ways to get the information you need. You can attempt to pass two consecutive Speech checks or challenge him to a game of dice.
If you prefer a more direct approach, you can also engage the miners in a fistfight. Failing the second skill check also leads to this scenario.
Joerg is a capable fighter, but only he fights, not all three. He will surrender at about 30% Health. The hardest part is you will likely not see much, because there is almost complete darkness in the hideout.
Regardless of your choice, Joerg reveals that they no longer have the standard. They sold it to a merchant named Hensel, who was last seen heading toward Prague by way of 
Bylany.
The best exit is the same way you came, through the tunnels, because one of Joerg's friends will run off to alert the guards.
Tracking Merchant Hensel
Leave the tunnels and travel south of Kuttenberg into the countryside. Search for clues along the road to find the merchant's trail.
Start at the western end of the area marked on your map.
Clues on the road:
- The bloody sack: Inspect the bloody sack on the ground.
- The wagon tracks: Follow the path south until you see wagon tracks leading off the main road into the forest.
- The abandoned cart: Following the tracks leads you to an abandoned cart. Interact with the cart to update your objective.
- The merchant's body: Locate the blood near the cart, then follow its trail, heading slightly south from the cart to find a pack of wolves.
If you are on a Lent (pacifist) run, do not kill the wolves with weapons. Punch them or use Mutt to help.
Inspect the body to confirm it is Hensel. You need to be out of combat to inspect. He does not have the standard.
Take a few steps southwest to reach a small cliff overlooking Danemark. You can descend for closer overlooks to inspect the next objective area (strong Far Cry-style vista scouting).
Optional missable task: Tragedy in Danemark
The clues lead further south to a mill. Bandits control the area and are hostile on sight.
This location contains the highly missable Tragedy in Danemark.
To start it, find the miller's family before you finish your objectives here. They are held on the upper floor of a shack near the northwestern gate. It is the right-most building in this screenshot:
A guard patrols, but stay in the river until he moves on, then use this ladder to reach the miller family:
Untie them and speak with them to begin the task: defeat all bandits in the area.
Yackers'n'Fash only needs the standard, but the task gives you a good reason to clear every bandit.
After the dialogue, the family heads for Maleshov and you do not need to escort them. If bandits spot you near the barn before the family leaves, they can climb up and kill the family, so avoid being seen.
After you speak with Miller Hermann, use 
Saviour Schnapps if you want a clean save before the fight.
The bandits are not particularly strong. Open combat, stealth, or ranged combat from the barn all work. From the barn you often have time to shoot with bow or crossbow before they regroup.
Loot priorities: Little John carries keys for the area. Speckles has a valuable Golden cup and Strong Saviour Schnapps.
There are about eight bandits total, but most wear little armor. After you defeat all of them, Tragedy in Danemark advances: pick up the reward.
Standard location: Enter the bottom floor of the southern building. The St. Anthony standard is in a Hard-locked chest on the right side of the room, near where the bandits piled the mill hands. The chest also holds about 320 Groschen and valuable trinkets.
Before leaving Danemark, grab the fast travel point at the river crossing; there is also a Laundry spot. Mutt may bark to highlight it.
Tragedy in Danemark reward
If you are quick, you can catch the miller still walking to Maleshov. Talk to him anywhere (bandits must be dead). He pays 150 Groschen, raises reputation, and the task completes.
Speaking to him again later lets you buy a bed at Danemark and learn a few skills.
Returning to Foreman Vlach
With the standard, return to the Black Horse Tavern in Kuttenberg to speak with Vlach.
The St. Anthony standard works as a blunt polearm. You can lie to Vlach and try to keep it, but that fails the quest and blocks the follow-up Striped Tonies side quest.
Handing over the standard completes Yackers'n'Fash. Vlach pays 250 Groschen. You also gain experience in Thievery, Scholarship, and Craftsmanship.
Yackers'n' Fash FAQ
Do I need Tragedy in Danemark for the standard?
No. You only need the hard chest in the southern building. Rescue the family first if you want the missable task and extra rewards.
Can I stack this with The German's Treasure?
Yes. Use the same river mine entrance and tunnel route; see The German's Treasure guide for maps and lock tips.
What if I keep the standard?
The quest fails and you cannot start Striped Tonies on that playthrough branch.
Where is Foreman Vlach?
Black Horse Tavern, western Kuttenberg, between 18:00 and midnight. He will not discuss the job while working at the mine during the day.
How do I get Joerg Preng to cooperate?
Two Speech checks in a row, a dice game, or a fistfight. Only Joerg fights; he gives up around 30% health. The room is very dark.