Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Global Position
GV_NEARESTPOINTONSPLINE_INPUT_GLOBALPOSITION
Parameter: Precision
GV_NEARESTPOINTONSPLINE_INPUT_PRECISION
Parameter: Spline Segment
GV_NEARESTPOINTONSPLINE_INPUT_SPLINESEGMENT
Parameter: All Segments
GV_NEARESTPOINTONSPLINE_INPUT_ALLSEGMENTS
Parameter: Spline Position
GV_NEARESTPOINTONSPLINE_OUTPUT_SPLINEPOSITION
Parameter: Nearest Point
GV_NEARESTPOINTONSPLINE_OUTPUT_NEARESTPOINT
Parameter: Nearest Segment
GV_NEARESTPOINTONSPLINE_OUTPUT_NEARESTSEGMENT
Parameter: Tangent
GV_NEARESTPOINTONSPLINE_OUTPUT_TANGENT