Expresses that something happens or is the case without a clear reason; often used when the speaker finds the situation puzzling or unexpected.
For some reason, the train is empty today.
Somehow, he suddenly got angry.
Kanji spelling using 訳; less common but still encountered.
Mixed kanji-kana form; rarely used.
Phrase composed of どういう (what kind of) + わけ (reason) + か (question marker). The combination literally means 'what kind of reason is it?' and has become a fixed expression for 'somehow' or 'for some reason'.