"SQL skills" is a bit of a trigger phrase for me because it's very much overloaded, since SQL work ranges from developing a database (that is, writing the database server itself) through designing a database (using a DBMS someone else wrote to implement a data system), through writing queries and doing DBA work. People tend to lump these things together without carefully understanding what job they're looking for (or what candidate they want to hire) or how to best build a data team or ...
Anyway! Since you asked specifically about querying, I can leave out all the rest:
A beginner:
- Knows the tool. Can setup and use a command-line tool, a GUI tool, knows a couple of each at least. Can diagnose connection problems. Understands how to save, load, manipulate files.