So, the things we don't know can be divided into things we can know but don't yet (Discoverable), those things we can never know (Undiscoverable), and those which can't matter whether we know or not (like Is your blue my blue), ie which have no know/don't know differentiation (Moot). I would set out that religion / faith / supernatural stuff is the domain of the Undiscoverable, science and rationality the domain of the Discoverable, and Philosophy the domain of the Moot.

-What happens inside a black hole: Discoverable.

-Does alien (as in, off-Earth) life exist?
   *Life on other solar planets: Discoverable.
   *Life outside the solar system: already so probable as to be certain, but, of course, the universe is so huge that it can't really matter either way, so I would score that as Moot.
      +If or when we discover that living molecules happen wherever their building blocks occur in planetary formation, the probability will asymptotally (is that the right word for ever-nearing never reaching?) approach the limit of certainty, but it's already pretty close to that limit anyway. Unless you want to discuss what is meant by "life" in the context of your question...

-"boundary" between thought and matter: Discoverable. I *think* we know that life is biochemistry and consciousness, electrochemistry of the biochemicals. Not sure whether "boundary" is the word I'd choose, though, perhaps interface?

At any rate, I don't see any rational need, yet, to posit anything worth having Faith about...