Ask your candidate how he proceeds when he has to make an important decision. What are his considerations and how does he reach a conclusion? Can he reason his decisions using valid arguments?
Try and find out what controversial ideas your candidate has when making decisions. Candidate: I always want to play it safe. Coach: How do you know you play it safe when you procrastinate making a decision? What do you need in order to gain more certainty? Candidate: I am afraid to make mistakes. Coach: Why are you afraid? What is the worst that could happen?
Encourage your candidate to ask others for 360º feedback regarding his decisiveness. What goes well and what could be improved? Discuss the results with the candidate.
Ask your candidate to describe a certain period of time when he had to make decisions and a period of time when he put off doing so. Discuss the results in order to reflect on the kind of decisions he finds hard to make, why it is so, and what can be done about it.
Try to find out together with your candidate what is keeping him from making certain decisions. Can the problem be found in his personality or in the subject?