Recently I saw the sentence「何見てるのよ」in manga. It was said by a female character. I suppose it's translated as "What are you looking at?". But I am not sure about the role of 「の」in this sentence. So there are 2 questions:
 1. Is 何見てるよ (without 「の」) still a valid sentence and means the same? 
 2. What 「の」particle means in this sentence? 

Also I've just found, that a 「の」particle can be used by feminine speakers as a sentence ending particle for emphasizing or questioning tone (which makes sense in the context of my question). But I am still not sure.