What interview questions should you ask when hiring a DevSecOps engineer?

Maybe I can give my thoughts on this. This is roughly what I would ask,
1. What experience do you have with DevSecOps?
2. Explain the DevSecOps workflow process you follow.
3. How do you ensure security in a DevOps environment?
4. How do you make sure that your DevSecOps practices stay up-to-date with the latest security 
    threats?
5. Describe the tools and technologies you use when implementing DevSecOps.
6. How do you identify security vulnerabilities in a DevOps environment?
7. What challenges have you encountered when developing DevSecOps solutions?
8. What strategies do you use to ensure compliance with security policies?
9. How do you keep track of code changes during the DevSecOps process?
10. How do you ensure that security is maintained throughout the deployment process?

What path did you take to arrive at becoming a DevSecOps engineer and what make you want to continue on this career path. 

We would pursue the software that the candidate is familiar with, specifically past accomplishments with examples of what was used, why, and how the project turned out. I would then discuss these with him/her to determine their full understanding of the process they may have used, what other options were available, what kind of things they'd do differently etc. 
This would continue in several directions to get a strong grasp of the candidates understanding of process as well as the software they are most familiar with and what they may be able to accomplish for you.

I would start to understand his background, why he is looking for a change and his most difficult project in this area.

After that I would ask some more specific questions:
– What DevSecOps tool have you work with?
– How can you help us with security aspects (some examples)? How do you prioritize security vs. programming agility?
– Knowledge about automation tools and language codes.

Apart from all kinds of questions related to the tooling they used and why, building the security in etc., I would these candidates through a "case study". They'll get a description of a real production problem we had in a form of "support ticket" and we will let them ask questions and "look into production" until they identify the underlying problem. In this first stage, we are able to observe how they approach the troubleshooting, confirm that they know which tools should be used for what, etc. Then, we talk about prevention – essentially, I'd let them "run the retrospective" on the problem. This allows us to see how they think about resiliency, automation, testing, and also when to invest and when it does not make any sense.