I am currently evaluating IoT platforms which can connect to devices and controllers, then collect data and do some analytics
To start with I have this device "JACE 8000" which runs on Niagara platform, which has communication protocols like obix, mqtt etc
I would like to know if Kaa already has any existing module or plugin for this? If not how to build a new one? and how easy is it to develop a new plugin
It appears that Kaa's preferred choice of protocol is MQTT. Niagara N4 happens to provide an abstract implementation of an MQTT driver, so I'm confident that would probably be your best route for development if you wanted a JACE to communicate with a Kaa network.
To go into any more depth is difficult here because you really need to be either a certified Niagara engineer or developer and have access to a workbench, documentation, and so on. The Niagara framework is a big beast!