Your question was closed because questions asking to identify specific movies, TV shows, or episodes are off-topic here, and have been for about two years now. It's unfortunate that nobody left a comment to that effect before the question was closed, but comments on downvotes/closevotes aren't mandatory, and for good reasons.
You would have received some feedback in the form of this close message, that I can see about your (now-deleted) question:
What must have happened, though, is that the question was deleted before you even knew it was closed, let alone had a chance to read that message.
In my experience, off-topic questions get closed and deleted very quickly on Movies.SE, which is both a blessing and a curse; a blessing because we don't have low-quality questions sitting around, and a curse because it leads to situations like this one, where people are left wondering where their post went.
As for your actual question:
what is the preferred feedback mechanism for newbies like me to learn from their mistakes in this situation?
Do exactly what you just did: post a question on Meta, calmly explaining the situation and asking what was wrong with your question and how/whether it could be improved. Someone will come along and help you out.