？
What sound do sheep make?
Literal
Sheep [topic-は] what-[manner-て] cry-[sentence-ending-の]?
何て ('how / what [kind of]') is a casual 'how' used in questions. 鳴く is the verb for animals vocalizing — crying, calling, barking, mewing. Different animals take 鳴く with different associated sounds (sheep: メエメエ). The の is the casual question ending.