反问【fǎnwèn】

A 反问 is a rhetorical question: it has the form of a question but makes a statement, and the statement is the reverse of the form. A positive question asserts a negative; a negative question asserts a positive. It sounds stronger than the plain statement and often carries surprise, impatience or reproach.

怎么 + 能 / 会

怎么能 asserts "should not", 怎么会 asserts "cannot be the case". A final 呢 is common.

哪儿 / 哪里

哪儿 or 哪里 before a verb, with no sense of place, means "not at all": 我哪儿知道 is "how would I know".

谁

谁 + 不 asserts "everyone"; 谁 + positive verb asserts "no one".

The two most frequent frames have their own points: 难道…吗 and 不是…吗. 何必 makes a rhetorical "why bother".

Getting the form wrong

A question word already makes the sentence a question, so 吗 cannot be added. 呢 or nothing closes it.

• × 我哪儿知道吗？ → 我哪儿知道？
• × 你怎么能这样做吗？ → 你怎么能这样做呢？

A 反问 is also blunt. Aimed at a teacher, a boss or a stranger, a plain statement is the polite choice.