  The $R_{D^{(*)}}$ anomalies are among the longest-standing and most
statistically significant hints of physics beyond the Standard Model. Many
models have been proposed to explain these anomalies, including the interesting
possibility that right-handed neutrinos could be involved in the $B$ decays. In
this paper, we investigate future measurements at Belle II that can be used to
tell apart the various new physics scenarios. Focusing on a number of $\tau$
asymmetry observables (forward-backward asymmetry and polarization asymmetries)
which can be reconstructed at Belle II, we calculate the contribution of the
most general dimension 6 effective Hamiltonian (including right-handed
neutrinos) to all of these asymmetries. We show that Belle II can use these
asymmetries to distinguish between new-physics scenarios that use right- and
left-handed neutrinos, and in most cases can likely distinguish the specific
model itself.
