Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Matrix Mode
GV_POINT_MODEParameter: Use Deformed Points
GV_POINT_USE_DEFORMEDParameter: Point Index
GV_POINT_INPUT_POINTParameter: Point Position
GV_POINT_INPUT_POSITIONParameter: Point Count
GV_POINT_OUTPUT_POINTParameter: Point Position
GV_POINT_OUTPUT_POSITION