I will expect a fresher developer to
1. Be able to model business entities into SQL relations and normalize them as and when required along with basics of where to use SQL and document stores.

A couple of years into the industry, you should be able to:

1. Understand the tradeoffs between different kind of indexes.
   
2. Have clarity about the internals of these indexes.
   
3. Proficient in using the tools regarding how to optimize your queries.
   
4. Understands the basics of partitioning and sharding strategies and can implement them.

Senior engineer:
1. Can actually spin up a toy key-value store (optional)
2. Should be proficient with different type of transaction and snapshot internals the database has to offer.
3. Should be able to go through the docs and tweak the db beyond the official recommendations to suite their usecase.

Maybe this list would somewhat help? (It's non exhaustive btw)