Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Global Position
GV_NEARESTPOINT_INPUT_GLOBALPOSITION
Parameter: Point Index
GV_NEARESTPOINT_OUTPUT_POINTINDEX
Parameter: Point
GV_NEARESTPOINT_OUTPUT_POINT
Parameter: Distance
GV_NEARESTPOINT_OUTPUT_DISTANCE
Parameter: Difference Vector
GV_NEARESTPOINT_OUTPUT_DIFVECTOR