質問だ

it's a question

→ 質問
phrase Common #6,487
it's a question 質問 means “question,” and だ is the informal copula meaning “is.” Depending on context, it can also be used emphatically as “that's a question.”
JA: それは難しい質問だ。
EN: That's a difficult question.

なんという質問だ

What a question!

— 惑星ソラリス (1972)

質問だドイツ覚悟

I've got a question for you, Germany: are you prepared?

— 帰ってきたヒトラー (2015)

よい質問だ

Good question.

面白い質問だ

That's an interesting question.

— ワン・バトル・アフター・アナザー (2025)

ばかばかしい質問だ

What a ridiculous question.

礼儀上の質問だ

It's a question of courtesy.

— ファイト・クラブ (1999)

どの質問だ

Which question?

— ブレードランナー 2049 (2017)

どんな質問だ

What kind of question is that?

— ブレードランナー 2049 (2017)

良い質問だ

That's a good question.

— きっと、うまくいく (2009)

質問だ

It's a question.

— Good Luck, Have Fun, Don't Die (2026)

やさしい質問だ

That's an easy question.

— ラブ・アクチュアリー (2003)

そりゃ難しい質問だ

That's a tough question.

— アメリ (2001)

実に鋭い質問だ

That's a very astute question.

— どん底作家の人生に幸あれ! (2019)

そいつはマジでいい質問だ

That’s a really good question.

— ドライヴ (2011)