Welcome to your interview.
The question is on your right: Real-Time Event Deduplication. 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.
Given an input stream of job application events, how would you deduplicate the data in real-time?