A JSONiq developer works with the JSONiq language, a query and processing language specifically designed for JSON data. They use this language to transform, aggregate, and filter data stored in JSON format, leveraging JSONiq's expressive and declarative capabilities. They are also responsible for parsing and updating JSON data. In addition to the core JSONiq language, they may work with extensions that allow interaction with NoSQL databases. Their goal is to extract valuable insights and facilitate data manipulation, often in contexts where large amounts of data are involved, such as big data analytics or API development.