On this page of the Disco Elysium guide, you will find a walkthrough for Ask Scab Leader about tattoos task.
The goal in the Ask 'Scab Leader' about tattoos task in Disco Elysium is to talk to the leader of the strike about the dead man's tattoos.
You will receive the task from Joyce Messier after you ask her what she knows about the deceased's tattoos. Then you have to pass the Logic skill check to find out where the other two mercenaries from Krenel's group are currently staying.
Go to the place where the strike is and talk to the man marked in the picture above. When you ask him about his late colleague's tattoos, the mercenary will tell you a terrifying story about one of the designs.