To feel doubt about something; to wonder whether something is true or acceptable; to be suspicious or have reservations.
その説明が本当に正しいのかと疑問に思った。
I wondered whether that explanation was really correct.
彼の行動には少し疑問に思う点がある。
There are a few things about his behavior that I find questionable.
説明不足で消費者が疑問に思うのは当然だ。
It's natural for consumers to have doubts when there's insufficient explanation.