PropagatorDenominator[q, m] is a factor of the denominator of a propagator. If p is supposed to be D-dimensional enter: PropagatorDenominator[Momentum[q, D], m]. What is meant is - ). PropagatorDenominator[p] evaluates to PropagatorDenominator[p, 0].
See also: FeynAmpDenominator, PropagatorDenominatorExplicit.
The FeynCalc Book | PowerSimplify | PropagatorDenominatorExplicit |