Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Create Tri-/Quadrangle
MDATA_ADDPOINT_TRIParameter: Polygon Type
MDATA_ADDPOINT_POLYTYPEParameter: Edge Position
MDATA_ADDPOINT_EDGEParameter: Position World
MDATA_ADDPOINT_POSITION