Deep dive into React, Node.js, Express, Sequelize/Mongo RESTful API design (GET, POST, PATCH, DELETE) Realtime systems (e.g., WebSockets, Kafka, Redis) Cloud basics (AWS EC2/S3, deployment strategy) Your project walkthroughs (e.g., “Explain how you built the backend for ventilator data ingestion”) Debugging: “You have a memory leak or heap out of memory issue. How would you handle it?”