Here is a picture of the transfer case of my Mk 5, the last time I had to have the floor up, with the dipstick circled in red. The front of the vehicle is towards the top of the picture (you can see the back of the handbrake assembly and the lower seat mounts), and the back is towards the bottom (you can make out the fuel tank, and the edge of the hole into which the commander's seat drops onto the spigot).
Normally, you would only open up the oblong access panel, in which case the dipstick is at the lower right of it and may be a bit hard to see (it's an oblong for a reason though). You need to unscrew it with a wrench.
Cheers,
Terry