How do you know the candidate?
How closely did the candidate work with you and for how long?
Were you the person that originally hired the candidate?
How much direction did they need to be successful?
How did they mature during their time with you?
What things did you witness that frustrated them?
How did they manage the pressure of the job?
What would you consider are their strengths, assets, things you like and respect?
How did they support their colleagues?
What were they known for?
What was (name's) biggest accomplishment while working for your company?
Why did the candidate leave the company?
Is there anyone else at your firm that you would recommend as a 2nd reference check?
Let me tell you more about the job they are applying for. How do you think they might fit in the role? Good fit indicators? Bad fit indicator?
How do you think the candidate will respond to an unstructured environment?
What do you think are the best way to manage and develop the candidate?
What advice would you have for on-boarding them effectively and getting them productive quickly?
Anything else you'd like to mention, that we haven't covered?
Would you rehire the candidate?
Any questions I haven't asked that I should?
Some questions taken from Topgrading and https://www.checkster.com/blog/best-reference-check-questions