—When is your birthday?

—At November 2nd.  

1. 用 at 错误。这里用 on 或不用。

2. 表示一天当中某个具体的时间点位，介词往往用at，时间名词前不加冠词。就像非常具体的钟点一样，如 at twelve o'clock。常见的还有：at ten, at dawn, at dusk, at noon, at night, at midnight, at daybreak, at sunrise, at sunset, at midday。