What questions should I ask to find out originality of students’ work? As a TA, I should review undergraduate students’ works, containing reports and computer codes in order to find out whether plagiarism or cheating occurred or not. I tried to use online and offline plagiarism tools without success. Finally, I decided to ask them a couple of questions about their works.

I was wondering if anyone suggests a couple of questions which can help me to find out whether they did their project by themselves or borrowed from a “friend”. In addition, I would like to weight their knowledge. How can I do that?

UPDATE: The course is "computer programming".
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?”