Please list the questions that interviewer must ask to judge the skills and suitability of a candidate for the role advertised.

I would suggest to go for Competency Based Questions or Behavior based question to assess the candidate suitability. Never opt for gut feeling. yes you may start with traditional and open ended questions but trickle down it to hit the competencies related to position.

There are some questions should be the interviewer ask for the seekers jobs, one of them and we can say this questions in common is( Talk about your self that means your experiences and skills not your personality life. Also, there is another one and need some one to explain  if he has any idea about it and what is the purpose from ask this question( why should I hire you in my company or wherever)