Used to ask about people. Can be used as subject or object. Forms questions with verb in third person singular. Informal speech uses "c'est qui qui" for "who is it who"
"Che", "cosa", and "che cosa" are all correct for "what" questions. "Cosa" alone became more common over time. Regional usage varies: "cosa" in Northern Italy, "che" in center-south. "Che cosa" is classic literary form valid everywhere