Core java: Very important to have good grasp of fundamental Java concepts. Aware of good coding practices. Knows how to use some of the design patterns and understands fundamental object oriented programming.
Spring and Spring boot :
You should be well versed with Spring framework and not just Spring boot. You should be able to demonstrate practical experience of building, maintaining and debugging applications built using these frameworks.
Persistance and ORM: Good hands on experience on ORM frameworks (hibernate, Spring data etc). Should be able to work with RDBMS db directly using SQL or NoSQL DB.
REST and web-services:
You should have experience building REST APIs and should be able to easily work with relevant tools and techniques like JSON, Postman/Curl
Cloud platforms (good to have) :
It is a big plus if you have exposure to any of the leading cloud providers (Amazon Web Services (AWS), Google Cloud Platform(GCP) or Azure). You should have understanding of how app is deployed in cloud infrastructure and how it works after deployment.
Apart from Java language, you should be able to clearly communicate in English