This page of our guide to Greedfall contains a detailed description of A Name for a Family companion quest commissioned by Vasco.
Where to start the quest? When you get to New Serene and talk to Constantin, talk to Vasco afterwards.
In New Serene, go and do a reconnaissance at the captain's office. Vasco will recommend you to get four sleeping potions. You can buy them from the nearest merchant or, if you have the right talent, brew them yourself. Now move to the tavern and then downstairs to the owner of the brothel, Dieter. You can convince him to help by using charisma, or by offering a bribe of 100 gold pieces.
Meet with Vasco - you can dress up as Nauta, wait for Dieter's daughter or come back later.
If you wait for Dieter's daughter, you'll enter the harbor at night. Jump over the fence nearby and find Vasco's personal file in the chest. If you end with being detected/ or fight Vasco will be a bit mad at you (-1 reputation with him). Anyway, you will quickly complete the quest. You will get 1000 XP and you +3 to reputation with Vasco.