I'm struggling to think of a context where you'd say this where you couldn't just say "I don't know (about) that thing" or "there's a thing I don't know".
That there is a thing is kind of implied.
I'm struggling to think of a context where you'd say this where you couldn't just say "I don't know (about) that thing" or "there's a thing I don't know".
That there is a thing is kind of implied.