Which GameObject renders the Camera feed in unity and how do I access the feed data?
The WikitudeCamera renders the camera feed.
To access the data as a Texture2D, you can use WikitudeCamera.CameraTexture property.
If you need to access the pixel data on the CPU, you can either use Plugins, or get it directly from the CameraTexture, as described here.
I tried to find WikitudeCamera.CameraTexture but no such thing in the SDK 9.2??
The documentation you linked actually mentions the "CameraTexture" (link).