Let us say that When a word is singular indefinite and not in a possessive form, and used in this sentence structure : X is Y , the word Y will have -un at the end , unless it was at the end of the sentence.
could one interpret this as it be said as a question as " you are a teacher, rania ? " or does it really need the word "hal" (هل) in the beginning to point out you mean it as a question.
Yes the clearer way to ask someone is, "are you a teacher rania?". However you can also say "you are a teacher Rania?" But you need to allow your voice to go up at the end so people know it's a question not a statement (it is seen as a softer way of asking the question).