Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Conic Type
CONICCURVE_TYPE
Parameter: Coefficients A,B,C
CONICCURVE_ABC
Parameter: Coefficients D,E,F
CONICCURVE_DEF
Parameter: Start Point
CONICCURVE_P1
Parameter: End Point
CONICCURVE_P2