I interviewed for a backend role at Cognizant, and one of the more in-depth areas they explored was around Node.js architecture and performance optimization. For example, they asked: "How many default worker threads does Node.js have?" "How does the event loop work under the hood?" "What is the role of libuv in Node?" They also tested my understanding of database concepts, such as: "What is indexing and the different types of indexes?" "Explain shading in databases." "Write a SQL join query." There were a few hands-on coding challenges too, like: "Print the second largest number in an array." And they touched on web security and fundamentals: "What is the difference between authentication and authorization?" "What are some common security practices in web development?"