Well, to put it precisely, an omniscient being would theoretically be capable of knowing today's state of the law with probabilities assigned to the results.

I'm serious. Pick any non-trivial issues of law, ask a world leading expert, and you'd very quickly hear the word "probably" somewhere. Less often than "it depends", but you'll hear those words often nonetheless.

If that's "knowable" to you, I guess it's knowable.