On this page of the Assassin's Creed Valhalla guide, you will find a detailed walkthrough description of the Pricking The Needle mission.
Eivor heads to the port of Jorvik in search of the steward there, who Ljufvina believes has a lot on his conscience.
Reward: 5100 XP.
Search the Trade Depot
The trade warehouse in Jorvik is a heavily guarded place, so it is crawling with Red Hand's men. The main entrances are obviously barricaded so you have to use an alternative entrance that leads through the roof.
When you examine one of the documents lying on the upper level of the room you will learn that the merchants' complaints had never reached the council.
In the main storeroom, you will find many requisitioned, highly valuable items, as well as a note stating that all of the money coming from the merchants is to be delivered to the exchange office daily.
Seek out The Needle
The port administrator requisitions goods and then sells them to the merchants in the marketplace. The stalls of those involved were marked with black cloth.
Head to the marketplace. On the spot, you will find two bandits who are talking about the evening meeting with Needle. One of them has a key that you will need. Take the key from him (you can steal it) or kill the bandits and take the item.
Talk to a merchant who deals in overseas goods. A black cloth was hung in front of the entrance to his booth. The man won't be too eager to talk, but there's a boy hanging around who clearly has something to say.
The boy will tell you that if you want to strike a bargain with The Needle, you must arrive at the statue near the east gate.
Explore the sewers
The entrance to Needle's hideout is through the building shown in the image above. Open the door, go inside and go down into the sewers.
The path continues through the wooden scaffolding where the black cloth was hung out. Then jump into the water and dive to swim to the rest of this location.
You will eventually reach a spacious room where The Needle's men melt silver into bars and mint coins from it. A guard with a key keeps moving around the mint grounds. Eliminate him, then open the door on the right side of the room. Inside, you will meet the port manager, Grigori - he is the one who hides under the nickname The Needle.
Confront The Needle at Coppergate Market
The Needle will exit through a side door and leave you in the company of his elite men. Defeat them, then exit the room and finish off the remaining guards.
Use the nearby stairs to exit the sewers and go straight to the Coppergate Market.
The Needle is accompanied by many guards, but you can easily get him by attacking from above. After the kill, the mission will end and you will receive 5,100 XP as a reward.