"Do you have my jacket and my skirt?"
Translation:Har I min jakke og min nederdel?
Yes, "du" should be accepted. Usually, the context will give a clue about the number people involved (du = 1 person , I > 1 person). When there is no context available, such as in this kind of exercise, you are free to choose. Note that many languages are quirky to this respect: to address one person there is a separate pronoun, but for groups of 3, 10, 1009, or whatever number, the urgency to distinguish is absent. Several languages, though, have words to refer to two people, e.g. "Jeg gerne, men vi er begge stadig forholdsvis unge (22 og 23)". Equivalents of "begge" in English, German, Dutch, and Italian are "both", "beide", "beide/beiden", "entrambi".