  We investigate theoretically non-magnetic impurity scattering in a
one-dimensional atomic topological superfluid in harmonic traps, by solving
self-consistently the microscopic Bogoliubov-de Gennes equation. In sharp
contrast to topologically trivial Bardeen-Cooper-Schrieffer \textit{s}-wave
superfluid, topological superfluid can host a mid-gap state that is bound to
localized non-magnetic impurity. For strong impurity scattering, the bound
state becomes universal, with nearly zero energy and a wave-function that
closely follows the symmetry of that of Majorana fermions. We propose that the
observation of such a universal bound state could be a useful evidence for
characterizing the topolgoical nature of topological superfluids. Our
prediction is applicable to an ultracold resonantly-interacting Fermi gas of
$^{40}$K atoms with spin-orbit coupling confined in a two-dimensional optical
lattice.
