Asking which month (e.g. "What month is it?/Which month?").
あなたは何月生まれですか。
What month were you born in?
来年の何月に日本へ行く予定ですか。
In which month next year are you planning to go to Japan?
夏休みは何月から何月までですか。
From which month to which month is the summer vacation?