One of GreedFall's more interesting systems is that you can disguise yourself if you need to sneak into an area. Dressing up is essential because when you're trying to help your companions or make them happy, you don't want to end up murdering many members of their faction. This system is introduced to you early in the game, as you walk through Serene before setting off for the New World.
GreedFall - Where to find Naut's costume in Serene
During the opening missions of the game, you will have to go to an area controlled by the Nauts. To do it safely, please Vasco and don't end up murdering a lot of people, you need a Naut disguise. The disguise system works as follows: If you are wearing a piece of chest armor belonging to a particular faction, you can trick members of that faction into believing you are part of it.
To find the Naut disguise, you need to go to the docks, open your map, and search for a building called the Storeroom. On the map, there is a group of three doors on the lower left and doors directly to their right. This is the storage room. You'll end up going there while you're looking for the missing Cabin Boy, but you can get there earlier if you want.
Enter and look for a chest in the room. Inside the trunk is a sailor's jacket. Wearing this jacket allows you to blend in perfectly with other Nauts. He also has good stats and is a solid armor for the start of the game.
If you want to check the faction of your chest armor in your inventory, open the Armor tab and navigate to the chest. Scroll through the armor list and you will find the little faction symbol on the armor stats.
There you have it, now you know where to find the Naut disguise and how to disguise yourself as a faction when you need it.