Disco Elysium's Cuno is a monstrous little brat, but there's also good reason behind it. Regardless of his home life, though, you've got to step up and show some force if you want to help Cuno - well, as much as you can - and complete his questline. Like much else in Disco Elysium, it's a delicate process and one you can lock yourself out of if you're not careful. You can help Cuno to an extent, though it takes a lot of work and a separation from Kim.
How to Deal with Cuno in Disco Elysium
You'll encounter Cuno when you investigate the corpse. He's pelting it with rocks and generally being a monster to you and Kim. There's a set of rules to follow when dealing with Cuno that keeps the relationship between you balanced and ensures you can both finish his quest line and even get the deviant on a good track at the end of the game.
First, though, you need to punch him when he accuses you and Kim of pedophiles. You'll also need to pass a strength check to do it. If you didn't build Harry around Strength when you started, check around the nearby cars for an equip-able item that boosts your strength, then hit the kid.
It seems harsh, but punching Cuno when the option arises is the only way to start earning his respect. If you don't, or if you fail the check, you're locked out of Cuno's quest and can't recruit him later.
Cuno Dialogue Options
In general, here's what you want to do when speaking with Cuno.
- insult him (other than, y'know, punching him)
- thank him
- speak against or harm Cunoesse
- try and change his viewpoint
- encourage his artistic side
- let him see the autopsy
- ask him about his name if the option comes up
- mention the pig head and say you liked it after visiting his shack (this isn't vital, but it does earn XP and some amusing reactions)
Some found success by not punching Cuno and using Empathy to get him away from Cunoesse, but this method is less reliable.
Split a Kilo with Cuno
Once Cuno respects you, he'll ask you to get some drugs from his dad's apartment. Get the boltcutters from Kim's toolbox if you haven't already, and head to apartment number 12. Grab the vial from the table, then take it back to Cuno. The next choices don't matter.
Cuno as a Party Member
If you finish Split a Kilo with Cuno and have his respect, you can recruit him as an assistant later on. To do that, though, you'll have to let Kim get shot after the tribunal. Cuno wakes you up and says Kim is dead (he isn't actually) and appoints himself your new helper.
After that, you can convince the Precinct to admit Cuno into the youth program. While you never see the effects of your actions, it's the only way to help Cuno out of his destructive spiral and abusive relationship with his father.