I can do adhoc mapping of the response using tExtractJSONFields.
I've imported a sample JSON response into a reusable File JSON metadata schema. I have no idea how to map either "string" or "body" response to a pre-defined metadata JSON schema. Is this even possible? I believe it's doable for XML using tXMLMap but nothing exists for JSON.
You will need to look at the tWriteJSONField component. Take a look here: https://help.talend.com/reader/KxVIhxtXBBFymmkkWJ~O4Q/50PMKM8mz4A5fAL~FQcLHw