You should follow this training path: it teaches about import and export mappings. These mappings turn your JSON string into a set of objects, which you can then use normally in your application.
You can write out a hardcoded import mapping or implement something more generic in Java.
There exists various JSON querying language like JSONPath, JaQL, and JsonQuery. Some of them are similar to XPath. Pick a library, e.g. and json-path/JsonPath implement a Java action. You can then store your queries in some table, build a front end for manipulating and execute it.
For ultimate visualization you can use Jelte Lagendijk’s excellent widget at JelteMX/mendix-json-widget