My friend is getting beer for me. I say:
Don't you need my ID?
Do you need my ID?
What's the difference and what would a native say?
They're both acceptable. "Do you need my ID?" suggests that you don't already know the answer. "Don't you need my ID?" suggests that you already think that he/she does need your ID but you want him/her to clarify.
I would use neither. In the UK, you have to show your own ID, not someone else's in order to buy alcohol. (Note that you only need to show ID if the bar staff think you appear to be underage.)
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.