Would you say that the following phrases are not interchangeable in any of their contexts:
don't you know
don't you know it
don't you know - 1. I thought you knew: 'We're supposed to either sign these contracts or rewrite them. Which is it?' 'Don't you know?'
2. (also: you know) is used as a rhetorical question: My wife is such a nervous woman, don't you know.
don't you know it - you can be absolutely sure about that; you're exactly right: 'Man, is it hot!' 'Don't you know it!'
P.S. How can I delete my previous messages