question, problem, doubt, guess
Example sentences
彼は今日学校にくるかどうか疑問だ。
I doubt if he'll come to school today.
彼はやたらに故事来歴に詳しいけれど、それが人生の役に立っているのかはなはだ疑問だね。
He has a great storehouse of knowledge about historical details but I seriously doubt that's of any use in life.
彼の成功には疑問がある。
His success is in question.