Open is not enough
An open question still needs a purpose.
In conversation
A question can invite a long answer without inviting a useful one. Begin with what you want to understand and then choose the wording.
Ask whether the candidate can recognise the situation you are referring to. Concrete context often helps a person provide a clearer account.
After the answer, review what has actually been established. The form of a question matters less than its relationship to the purpose of the conversation.