In general a JSON is also just a string.
When talking of the ctrlX Data Layer there are some data stored as flatbuffer. How wor with this you can see as some examples in this thread.
If you really want to use the functions of the Data Layer is possible via the standard interface that is also available via the REST API. The more common way in my opinion would be to use the CXA_MOTION library. There are functions for commanding included:
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