There are none. That is, it's not part of the public API. Plugins rarely are, but for most plugins we publish the source code. The VASP one is different (for various reasons), so you can't read the source.
You can reverse-engineer it quite a bit tough: you see the filenames in the AddOn directory (like Analysis.pyc). Now you can, in atkpython, do
import AddOns.VASPPlugins.Analysis as a
print dir(a)
Then you can pick a function, like createVASPDensityOfStates and do
help(a.createVASPDensityOfStates)
Best I can offer, for now