On the Q&A site OKWAVE, it says that its purpose to help people resolve their questions and/or problems, and it uses 悩み and 疑問.
According to Weblio, 悩み has the meanings of “trouble(s), worry, distress; agony, anguish; a problem”, and 疑問 has the meanings of “(a) doubt; a problem, a question”.
Does anyone know the difference between these two terms?