Pseudodragons have spell resistance 12.
As a familiar, at level 11, it gains spell resistance 16 that scales with the wizard's level.
Do the spell resistances stack?
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As with all typed bonuses, you will only have the higher of the defenses. In this case, offenders would only need to roll once, against SR 16.
Specifically, from Spell Resistance
Spell resistance does not stack, but rather overlaps.
So, if for some reason it lost access to your Wizard class feature SR, it could still have its innate SR.