First mentioned in:
To acquire a skill, you must make a coin Bingo on a skill note. Once you've got a skill note, aim for killing as many special officers and opening any treasure chests you may come across to increase your chances of coins. Furthermore, any time you see (Recommended!) over a character, use that to increase your chances as well for coins to drop. This will require at minimum two Skill Notes, as the maximum you can get from one card is eight, but you can definitely mix and match as long as you're still getting coins from your runs through the episodes (and you will be playing the episodes quite a lot to get that Platinum).