As a general rule, I tend to stay away from such technically detailed questions. I strongly recommend using behavioral style interview questions to understand the person's history and what they've accomplished, the challenges, they faced and how they overcame them. These usually take the form of "Tell me about a time when..." or "Give me an example of..."
Q: Tell me about a time when you had to do an integration involving REST APIs.
You'll know immediately if they have or have not done it. If they have, you can go deeper on that topic.
Q: What challenges did you encounter? (and how did you overcome them)?
Q: What tools did you use?
Q: Had you done REST APIs prior to this project?
You're not trying to determine specifically how much they know about REST (or SOAP), but trying to determine if they can solve technical problems quickly. That's a more valuable skill than specific protocols because the protocols of tomorrow will require someone can learn fast and adapt.
