Dsa( array and string based medium questions), Core java, streams, Spring Boot, all annotations in spring boot, multithreading, data jpa, hibernate, aop, transactional, bean lifecycle, dependency injections, exception handling, security, junit and mockito, design patterns( atleast 5 6), solid principles, sql, indexes, queries on joins, microservices, kafka, microservices design pattern, circuit breaker, communication between microservices (synchronous and asynchronous), git commands, deployment pipelines, some cloud knowledge, docker commands, system design(high level and low level), cap theorem, hashing techniques, database sharding like concepts.
This all you need to prepare. I was asked all these in all the rounds combined. Total 5 rounds were there