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.
The documentation you linked actually mentions the "CameraTexture" (link).
Which GameObject renders the Camera feed in unity and how do I access the feed data?