"Does the sheep drive?"
I've asked that from a native speaker and he said that: 느냐 is kind of old style of speaking, we don’t say nowadays. And usually king, royal family’s questioning word long long time ago. (When Person who is in a higher class asked to the person who is a servant)(or when older person asked to youngers) it’s a old-fashioned word. If you say this word, native speaker would laugh and think you are making a joke) : ) 니 is questioning word in Informal way
I guess you're thinking about the so called quotative (sort of like reported speech) construction? That is indeed this form + -고, and the result can be used in a bigger sentence: 난 친구에게 양이 운전하느냐고 물었어 "I asked a friend if sheep can drive". In colloquial speech the -고 seems to be optional; I guess this is where your confusion comes from. But without -고 the sentence can also stand on its own, although it is casual to the extreme.