What is the maximum possible number of passive skill points?
In short, it depends on the choices you make throughout the game.
Players can gain 99 passive skills points from levels and an additional 22 or 24 points from quests, depending on the choices you've made in the "Deal with the Bandits" quest.
In Addition, if you choose to play as a "Scion" you may gain up to 5 skill points depending on how you've allocated your ascendancy points.
Passive Skill - PoE Wiki
This is current as of version 3.0 Fall of Oriath