I'm with Silverthorne on this:
Knowing that laws exist, and roughly what kind of punishment you can expect for breaking them, is a function of Knowledge - Culture.
Knowing how the law works, and the specific details and exceptions, is the job of Knowledge - Law. This would tend to be known only by lawyers and law enforcement professionals.
For example, as a 33 year old Briton, I know a lot in general about this country's laws. I know that burglary, robbery, murder and incitement to racial violence are all frowned on, but little about what to expect if I am accused of it. I am not a lawyer, hence I need one to tell me what my rights were in the event of me "helping the police with their enquiries." I have no idea of specific punishments (all get imprisonment, but how much?).
A Federation citizen with Culture (Klingon) might know that killing in a duel is acceptable on Qo'noS, but not the specifics of making it a legal duel (i.e. just calling them out and then shooting them might not be acceptable). If he had Law (Klingon) then he knows the dividing line.
I'd guess that across the Federation there will be differences, although I note that the description of the Law skill lists specialties like Federation. That implies a certain amount of generalisation of legal systems across the Federation - Culture, or possibly Specific Planet, might then be needed to provide a "synchronicity bonus" (in knowledge rather than game terms) to know a specific twist. For example, Law (Federation) and Specific Planet (Betazed) might be required to know that telepathic rape will get you ten years of compulsory counselling on the Betazoid Homeworld...
Jon
"There are worlds out there where the sky is burning, where the sea is asleep and the rivers dream; people made of smoke and cities made of song.
Somewhere there's danger, somewhere there's injustice, and somewhere else the tea is getting cold. Come on, Ace, we've got work to do."
THE DOCTOR, "Survival" (Doctor Who)