  It has been well established that the $f$-mode of relativistic ordinary-fluid
neutron stars displays a universal scaling behavior. Here we study whether the
"ordinary" $f_{\rm o}$- and "superfluid" $f_{\rm s}$-modes of superfluid
neutron stars also show similar universal behavior. We first consider a simple
case where the neutron superfluid and normal fluid are decoupled, and with each
fluid modeled by a polytropic equation of state. We find that the $f_{\rm
o}$-mode obeys the same scaling laws as established for the $f$-mode of
orindary-fluid stars. However, the oscillation frequency of the $f_{\rm
s}$-mode obeys a different scaling law, which can be derived analytically from
a homogenous two-fluid stellar model in Newtonian gravity. Next the coupling
effect between the two fluids is studied via a parameterized model of
entrainment. We find that the coupling in general breaks the universal behavior
seen in the case of decoupled fluids. Based on a relativistic variational
principle, an approximated expression is derived for the first-order shift of
the $f_{\rm s}$-mode squared frequency due to the entrainment.
