なのかい

is it?

→ だ
phrase Rare #27,319
is it? An informal way to ask a question, often with a masculine or older-sounding tone. It follows a noun or a な-adjective.
JA: 君も行くなのかい?
EN: Are you going too?

そうなのかい?

Is that so?

— ドライヴ (2011)

彼女はまだ君の事外国人扱いなのかい?

Does she still treat you like a foreigner?

— Article 15 (2019)

まだ先なのかい?

Is it still a long way off?

— ロード・オブ・ザ・リング/二つの塔 (2002)

でも学校を抜け出したその子なのかい?

But is that the kid who ditched school?

— ほんとうのピノッキオ (2019)

それも演技なのかい?

Is that an act too?

— オープン・ユア・アイズ (1997)