Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Degree
NURBSCURVE_DEGREE
Parameter: Points
NURBSCURVE_POINTCOUNT
Parameter: Start Parameter
NURBSCURVE_TMIN
Parameter: End Parameter
NURBSCURVE_TMAX
Parameter: Closed Spline
NURBSCURVE_CLOSED
Parameter: Polynomial
NURBSCURVE_POLYNOMIAL
Parameter: Periodic
NURBSCURVE_PERIODICITY