How to retrieve 'Release Key' of a process for on premise version of Orchestrator

Hi all,

I want to execute XYZ (start a job) process from Orchestrator using Orchestrator API. I am following the documentation ( I have implemented authentication part and retrieved all the processes & Robot Metadata. I want ‘Release Key’ of the process which I want to start by using Orchestrator API.
This is the JSON input to the web service call:

{ "startInfo":
   { "ReleaseKey": "f689e02d-f968-494f-8b37-409a1bd85534",
     "Strategy": "Specific",
     "RobotIds": [ 9826 ],
     "JobsCount": 0,
     "Source": "Manual" 

Can anyone help me to extract 'Release Key' of any given processes or all processes present on Orchestrator.