Both are fine, natural, and could be said that way by a native speaker. I personally (US native) would probably say "How many hours of sleep do you get?" I would not bother to say "at night" unless the context made it necessary. I think the reason I would say "get" is that sleep is something that people "need" and try to "get." I personally would _answer_ the question by saying "I average six or seven hours a night, but I often take an afternoon nap as well."

You could say: How many hours' do you sleep? ('At night' would be assumed.) How much sleep do you get? How many hours' sleep do you get?

Long time no see, Jessicamessica. You can also say "How long do you sleep?"

How long do you sleep every night? How much do you sleep every night?