疑問に思う

wonder

→ 疑問
phrase Rare #32,699
wonder Used when wondering about or questioning something, often followed by かどうか (“whether”) or a question word. It can also imply doubt about something.
JA: 彼が本当に来るのか疑問に思う。
EN: I wonder whether he will really come.

理由を疑問に思う

I wonder why.

— セッション (2014)

それが真実かどうか疑問に思う

I wonder if that's true.