Dark Law: Meaning of Death/Jobs

Only certain jobs are available for any character at a given time. The availability seems to be based on the character's stats, the abilities they know, and their level.

Jobs affect what you can equip, which abilities you will learn, how your stats change, and how much money you receive when you level up.

"?" in the Income column indicates a random element. The value of this is (obviously) random, but apparently it's tied to your character's level - your earnings increase as you level up. A thief, for instance, can earn about 350 gold by level 20.