All State, Agent, and Activity Profile API data is visible and can be clicked into for more detail on the debugging page. This is especially useful for developing and troubleshooting arbitrary non-statement data sent to the LRS. You can access the debugging page by clicking on the 'beaker' icon at the top right of the screen.

About document APIs:

There are 3 document APIs that provide document storage for activity providers and agents. These are the State API, Activity Profile API, and Agent Profile API. 

The State API is scratch space for activities that do not have their own internal storage or need to persist state across devices. Similarly the Activity & Agent Profile APIs allow for arbitrary key/document pairs to be saved which are related to an activity or agent.