Politeness is a question of culture more than language, so it's difficult to answer without knowing where in the world you are and what kind of organisation you're working for. To me (native UK English speaker) both sound awkward and overly polite.
In both cases you're phrasing a question as a statement about that question, which makes it more difficult to understand.
You seem to assume that it might be rude to ask why you have been demoted, whereas I would expect to have a right to be informed of the reason for my demotion and would consider it very rude of my employer not to have already told me. I would certainly never call my employer sir, although I would call a customer sir.
I would probably just say
Would you mind telling me why I was demoted?
Could you please tell me why I was demoted?
but then I'm used to a pretty informal work culture. Your situation may be different.