There isn't a field for the currently tracked image target, but you can get this information by subscribing to the OnImageRecognized and OnImageLost callbacks on the ImageTrackable.
You can see an example of this in the following scenes: "Image Tracking - Multiple Targets", "Plugins - Advanced Custom Camera" and "Image Tracking - Extended Tracking".
Thanks for the response! I actually got it working all good.
All I want to do is get the currently tracked image target ID, name etc... in Unity runtime but I dont know how to get the currently tracked ImageTarget data from the trackable class? Shouldn't there be a public method in the ImageTrackable class that allows me to access the currently tracked image target?
A code example of how this works be awesome!