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The formula for saving throw DCs for critical hit effects is 10 + half of the weapon's item level + one of the attacker's ability score modifiers--the ability score normally used to attack with the weapon, unless stated otherwise.
But that's the answer from the CRB, so if the critical hit deck uses something different I don't know it.
This information can be found exactly where you'd expect it: In a small sidebar on page 181, which is neither the page with critical hit rules nor the page with special critical effects. To be fair, it is the page with weapon special properties, which use the same DC.