Good "I see you used technology X on this project - why did you pick that? how did it work out?" "What was a tricky or interesting problem you had to solve for this project?" "Can you tell me about how you handled XYZ in this project?" "Did you learn any lessons from the project? Would you do anything differently next time?" "Feature X is cool - how does that work?" etc etc. Or perhaps the most vague question of all: "Tell me about the project". In this case, I'd start with a high-level overview (the goal of the project, basic functionality, the technologies used), sketch out how the components of the project relate to each other (e.g. "there's a React frontend which talks to a Node backend via REST, and a Postgres database"), and ask if there's a particular part they want more detail on. I think you need to be prepared to talk about any aspect of the project, and to demonstrate that you understand it. That might just be some high-level / overview-type questions, or it might get down into the code itself. Ideally, you want to get into a natural conversation with the interviewer, where they become interested about a certain aspect, and you get to show off your knowledge and experience, and maybe even teach them something they didn't know.