• explain benefits and drawbacks of hashmap
• explain one way a hashtable works
• what is DFS and what is BFS
• in a BST, when you remove a node with only 1 child, what should you do
• design a recruiting portal where applicants can apply for jobs and recruiters / managers can post and manage applicant pools
• behavioural questions and experience questions to gague ability to pass system design interviews

need to know latency and throughput numbers for systems you've designed, tradeoffs, testability etc.