It seems to me the whole discussion in that chapter is about how to set up a phenomenological method to compute the conductance and current (or the scaling of these quantities) for strongly correlated systems or Luttinger liquids.
This is not what ATK is about; for strongly correlated system you need much more sophisticated methods, and hence you either can do only very few atoms, in some GW/many-body calculation, or you resort to a more phenomenological description. In such, you often employ "effective" parameters, such as various coupling strengths and correlation lengths, Fermi velocities, etc, without ever really worrying about how to compute them for "real" systems; just be assuming some values, you can still do interesting physics :)
ATK is sort of the opposite of this; by using a bit simpler models, it can handle real systems, without effective parameters, and compute the real current and conductance (as real as it can be considered to be within the model framework).
Nevertheless, ATK computes the kinetic Kohn-Sham energy; it is printed to the screen if you run calculateTotalEnergy() under verbosity 10, so:
import ATK
ATK.setVerbosityLevel(10)
E = calculateTotalEnergy(scf)
I'm not at all sure if this is the same "kinetic energy" as used in the Luttinger liquid vocabulary, however... And I'm even less sure if it makes any sense to couple to two approaches this way :)