Translation guide
A rhetorical question expressing that the speaker has no way of knowing the answer, often with irritation or exasperation. In Japanese, this is typically expressed with set phrases rather than literal translations.
Express that the speaker cannot possibly know the answer, often with annoyance.
Very blunt and rough. Used mostly by men in casual, irritated contexts. Literally 'Know? (sarcastic)'.
あいつの居場所なんて知るか。
How should I know where that guy is?
Common casual phrase meaning 'I don't know (and don't expect me to)'. The よ adds emphasis and can sound dismissive.
そんなこと知らないよ。
How should I know about that?
Stronger than 知らない; 'There's no way I'd know'. Casual.
彼が何を考えてるか知るわけないよ。
How should I know what he's thinking?
Polite form of 知るわけない. Can be used in formal situations but still conveys 'there's no way I would know'.
その件について私が知るわけがありません。
How should I know about that matter?
Very strong and dismissive; 'What do I care?' or 'It's none of my business'. Used when the speaker is annoyed at being asked.
お前の都合なんて知ったことか。
How should I know about your schedule? / Like I care about your convenience.
Imply that the question is unreasonable or that the speaker is not the right person to ask.
Literally 'Why are you asking me?'. Direct and natural in casual speech.
なんで私に聞くの？知らないよ。
Why are you asking me? How should I know?
Polite way to say 'Even if you ask me, I'm at a loss'. Implies the question is misdirected.
私に聞かれても困ります。担当者に確認してください。
How should I know? Please check with the person in charge.
Direct translations like どうやって知るべきか (dou yatte shiru beki ka) are unnatural and not used. Japanese uses set phrases to convey the rhetorical meaning.
どうやって知るべきか
how should I know (literal, unnatural)
知らない (shiranai) is a simple 'I don't know'. 知るか (shiruka) is rough and dismissive. 知るわけない (shiru wake nai) emphasizes impossibility. Choose based on the level of irritation and formality.
A: 鍵どこに置いたっけ？ B: 知らないよ。
A: Where did I put my keys? B: How should I know?
A: 会議は何時から？ B: 知るか。俺は呼ばれてない。
A: What time does the meeting start? B: How should I know? I wasn't invited.
A: 明日雨降ると思う？ B: 私が知るわけないでしょ。天気予報見て。
A: Do you think it will rain tomorrow? B: How should I know? Check the weather forecast.