。
Is she going to America next year?
Literal
She [topic-は] next-year America [to-に] go [explanatory-の] [probably-でしょう] [question-か]?
のでしょうか combines the explanatory の with the polite conjecture でしょう and question か — a very polite way to seek confirmation about someone's plans. More tentative and respectful than 行きますか.