we have a requirement for showing presentation on a wall through Spark Room Kit and not on Computer /Laptop.
Firstly, can we connect second external camera on to Spark Room Kit .
Secondly, if yes , can we achieve this using camera from cisco or need to buy some 3rd party camera.
there is one HDMI input on the Room Kit - that can be anything you want, PC, camera, etc. If you connect a camera you will need to control it externally, there is no pairing from an external camera to the unit for camera control.
What is creting the presentation on the wall, and what is showing it on to the wall? If it is some kind of projector, then that would likely be receiving its input from some other device, which could be split closer to the source as and used as a content input to the codec which would give your far end a better view of the content than that which you may achieve using a camera. However, if you need to get a person who may be presenting in front of something, then a camera may be a better choice (and, as @PJMack said, you can just feed the camera in as content input). A better choice if you are wanting to have presenter cameras would be a different codec (not the basic Room Kit) which supports the Presenter Track feature with an additonal Cisco Camera.