Welcome to your interview.
The question is on your right: Spark Broadcast vs Self Join. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
Explain the difference between a broadcast join and a self join in Apache Spark, and when you would use each.