Where to Find Skill Books
The books that give bonuses to stats are scattered all over the place, there are some places where you can get quite a few though.
The linlang temple has a lvl 5 chest with the +10 books to every weapon.
Various pharmacies and medical characters have medical books you can trade with or get from quests.
If you’re looking to pump up fist and are in the old man’s sect, when you open up his store he sells fist, blade, long and sword.