In the original Dungeon Siege II vanilla game, there is no built-in feature to reset or reallocate your skill points once you have confirmed them. You can only reset points immediately during a level-up before hitting the "Confirm" button.

The Vanilla Constraint: Permanence and Consequence

Since official options are limited, most players use mods to enable full respeccing: DS2BW-ResetPoints (GitHub)

Resetting Skill Points in Dungeon Siege 2: A Game-Changer for Players

Conclusion: Does Dungeon Siege 2 Reset Skill Points Work?

Yes – but only for Combat Powers via the Tome of Experience.
No – for General Skills in the vanilla game.

Function: This NPC resets all passive skills learned and returns the points spent, though it does not reset racial skills. Community Mods