Could you tell me what time the train departs?

Literal

Train [topic-は] what-time [at-に] departs [question-か] tell-me [favor-くれませんか].

A polite request built on an embedded question. 教えてくれませんか ('won't you teach/tell me?') is the ~てくれる favor-form + negative question, the standard pattern for polite requests. The negative politely softens the ask.