What questions should I ask to find out originality of students’ work?
Asking alot of questions can generally rack out the ones who did the projects themselves and ones who didn’t.

Questions can be just simple ones like “how did you this?” or you can ask further questions based on their replies, e.g., if they answer with “Using technique A”, you reply with, "Oh I see, how do you use technique A?” or “How does it work?”