Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Conic Type
CONICCURVE_TYPEParameter: Coefficients A,B,C
CONICCURVE_ABCParameter: Coefficients D,E,F
CONICCURVE_DEFParameter: Start Point
CONICCURVE_P1Parameter: End Point
CONICCURVE_P2