Is this a SQL Developer role specifically? If so, these are pretty common topics that are typically asked about:

• Difference between Primary Keys and Foreign Keys
• The different join types. Specifically, the difference between INNER JOINs (aka JOIN) and OUTER JOINs (i.e., LEFT OUTER JOIN aka LEFT JOIN or RIGHT OUTER JOIN aka RIGHT JOIN). Sometimes FULL OUTER JOINs are asked about too, but this is rare.
• Difference between a Clustered Index and a Nonclustered Index
• The purpose of a GROUP BY clause and when to use a HAVING clause versus a WHERE clause
• Window Functions (classic ones are ROW_NUMBER() and RANK())
• The purpose of a DISTINCT clause
• The purpose of a TOP or LIMIT clause (depending on the database system, but they mean the same thing)
• Less likely, but also possible that you could be asked about the UNION and UNION ALL clauses, their purposes, and differences between each other.