SOD[q] is a D-dimensional scalar product of OPEDelta with q. It is transformed into Pair[Momentum[q,D], Momentum[OPEDelta,D] by FeynCalcInternal.
Overview, OPEDelta, Pair, ScalarProduct, SOD.
SOD[p]\Delta \cdot p
SOD[p - q]\Delta \cdot (p-q)
SOD[p] // FCI // StandardForm
(*Pair[Momentum[OPEDelta, D], Momentum[p, D]]*)