Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Degree U
POLYNOMSURFACE_UDEGREEParameter: Degree V
POLYNOMSURFACE_VDEGREEParameter: Points U
POLYNOMSURFACE_UPOINTCOUNTParameter: Points V
POLYNOMSURFACE_VPOINTCOUNTParameter: Closed U
POLYNOMSURFACE_UCLOSEDParameter: Closed V
POLYNOMSURFACE_VCLOSED