Good or Best Quality Cranial Implants function as a cogitator. Per IH pg 146, a cogitator gives +10 or +20 on relevant tests.

1.) Do the Cranial implants give +10 OR +20?

I'd say +10, as they probably don't have the same amount of data stacks available to reference.

2.) What are relevant tests? All Int tests? Only trained Lore skills?

It seems like may GC Cranial implants give +20 or +30 to all known Int skills (Unnatural Int + cogitator bonus). That seems really, really good. Am I missing something?

Probably the fact that they're also really, really rare. We're talking "Get murdered by a Magos because he's jealous of you"-rare here.

Other than that, I'd assume that the mechanical effects of the cogitator are already included into the Unnatural Int (though that one is very debateable) - it's just that you essentially always have access to a computer, with all that entails: data storage, calculating stuff, running downloaded programs, playing a quick game of tetris,...

Radomo said:

I allow GQ cortex implants to count as a personal cogitator for that +10 bonus. It means a magos doesn't have to carry around the cogitator with him, he has one in his head.

Radomo said:

I can't find my copy of IH, but I'm pretty sure it's logic and scholastic lore tests.

Based on the exact phrasing of the entry, I'm inclined to agree that the cogitator-ness is not intended to confer any additional bonus, since they chose to refer to "functions" and not "benefits" or "bonuses". What it means, I think, is that you can store and read data, access networks, perform computations, and so on.