Для образования Present Perfect Continuous используем формулу: have/has + been + Ving.
В данном случае подлежащее Who, следовательно, используем has.
Who (sleep) in my bed?! It's all wrinkled! - Who has been sleeping in my bed?! It's all wrinkled!
Ответ: Who has been sleeping in my bed?! It's all wrinkled!