  The transport coefficients of quark matter at non-zero chemical potential and
temperature are computed within the two-flavor Nambu--Jona-Lasinio model. We
apply the Kubo formalism to obtain the thermal ($\kappa$) and electrical
($\sigma$) conductivities as well as an update of the shear viscosity ($\eta$)
by evaluating the corresponding equilibrium two-point correlation functions to
leading order in the $1/N_c$ expansion. The Dirac structure of the
self-energies and spectral functions is taken into account as these are
evaluated from the meson-exchange Fock diagrams for on-mass-shell quarks. We
find that the thermal and electrical conductivities are decreasing functions of
temperature and density above the Mott temperature $T_{\rm M}$ of dissolution
of mesons into quarks, the main contributions being generated by the temporal
and vector components of the spectral functions. The coefficients show a
universal dependence on the ratio $T/T_{\rm M}$ for different densities, i.e.,
the results differ by a chemical-potential dependent constant. We also show
that the Wiedemann-Franz law for the ratio $\sigma/\kappa$ does not hold. The
ratio $\eta/s $, where $s$ is the entropy density, is of order of unity (or
larger) close to the Mott temperature and, as the temperature increases,
approaches the AdS/CFT bound $1/4\pi$. It is also conjectured that the ratio
$\kappa T/c_V $, with $c_V$ being the specific heat, is bounded from below by
$1/18$.
