。
Does she have a piano?
Literal
She [topic-は] piano [object-を] has [question-か]?
持っている ('to have, possess') uses the resultative ~ている — 'is in the state of having.' This pattern applies to verbs of acquisition or change-of-state: once you've come to have something, the resulting state continues. Try the alternative 持つ alone and the sentence sounds odd; possession sits in the resultative form by default. か rounds out the question.