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You find the JSON in the display pattern editor in JSON preview: 
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kind: shows the type of content, e.g., ContentDoc for content items or ListItemDoc for list items.
fileTransferId: shows all assigned contentPermissionSets
ownerTokenId: shows the id of the owner
contentType: shows the type of content, e.g., File or Virtual
backup information
contentSchemaId: is the underlying schema of type file type or virtual type with the assigned layers.
In data, you find all available metadata values from the item
brokenReferenceIds, RelationTargetIds, and IndirectReferenceIds are for system checks to ensure data integrity. You can use those fields to check for any broken references in the system to fix them.
lifeCycle: is the state of the item, whereas inactive items are no longer available in the system
id: the ID of the item which is also shown in the URL when opening the item in the item detail view
docType: refers to the kind and the corresponding index in the database, e.g., ContentDoc or ListItemDoc
audit: shows information about creation and modification.
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You can see the JSON of an item by{ opening up the item detail view and check in the developer tools (Chrome F12) in the network the response for the corresponding item, shown as id: 
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