Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: GroupA
INT_GROUPAParameter: GroupB
INT_GROUPBParameter: Distance Type
INT_DTYPEParameter: Distance
INT_DISTANCEParameter: Particle Count A
OUT_INTERACT_PARTICLECOUNT_AParameter: Particle Count B
OUT_INTERACT_PARTICLECOUNT_BParameter: Position A
OUT_INTERACT_POSITION_AParameter: Position B
OUT_INTERACT_POSITION_BParameter: Vector AB
OUT_INTERACT_VECTOR_ABParameter: Distance AB
OUT_INTERACT_DISTANCE_AB