Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Variable Tag
FIELDLAYER_WEIGHT_LINK
Parameter: Mode
FIELDLAYER_WEIGHT_MODE
Parameter: Radius
FIELDLAYER_WEIGHT_RADIUS
Parameter: Distance Falloff
FIELDLAYER_WEIGHT_DISTANCEFALLOFF
Parameter: Use Deformed Points
FIELDLAYER_WEIGHT_USEDEFORMED
Parameter: Constant Update
FIELDLAYER_WEIGHT_CONSTANTUPDATE