I assume you are not coding this yourself.. it's one of the built in Rest services? It's not custom....
I would THINK you would need to use Dojo to call that... maybe in onClientLoad... or in a button... but the CSJS dojo would call it and get the JSON data... then put into a local Javascript variable... then you do an XSP.PartialRefreshPost.. or better yet a RPC call from CSJS to get the data into the viewScope...
Though when you type it out that seems a little on the silly side unless theres a reason... would it not be better to just create the JSON in SSJS or Java and then do whatever with it? In SSJS there are functions like toJson() that are available...
Just some thoughts...
Good Luck