Here's something I tried out. I basically tried to think of every single thing that might be cool to have a skill for. I used "traits" as the name for it, but that's just a placeholder.
All of these can be renamed to fit your character. For example, rejuvenate can be used both on a doctor character, a musician or a cook. Connections can be used by a former Marine, an underground broker or a politician. Persuade can be used by a charismatic leader, a feared criminal or a hypnotist. Most, if not all traits will require you to specify your range. If you are a pirate, connections might not let you get information on Marine bases. If you're a shipwright, upgrade might not work on a fridge. Also, some traits will share a lot of similarities, like information traits, but it's the way you use them. For example, Connections and Book might seem better than Forecast and Log Pose, since it allows you to know about anything, but Forecast might be better given the right situation, as it needs no external source (Connections needs the Player to talk to certain type of people). Usually, the more specific you make a trait, the more useful it will be when it can be used. Having a fishman character use Connections on other fishmen will probably not yield the same results as having a fishman politician from East Blue use Connections on another fishman from the East Blue who voted on you.
Remember! You don't have to have a trait to do all of these things, but it will make it a lot easier and have higher rates of success.
Persuade - can influence NPC:s to do things
Interrogation - can get useful information from NPC:s
Sneak - can avoid being seen by NPC:s
Connections - can get useful information from a certain crowd
Map - can get useful information about locations and places on the island
Log Pose - can get useful information about the Grand Line and nearby islands
Forecast - can get useful information about weather, the sea and climate
Blueprint - can get useful information about machinery and weapons
Sabotage - can hamper stuff
Upgrade - can enhance stuff
Poison - can harm or weaken people
Rejuvenate - can heal or enhance people
Steal - can buff things using knowledge previously discovered