Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Particle Object
FIELDLAYER_PARTICLE_OBJECTParameter: Mode
FIELDLAYER_PARTICLE_SOURCE_MODEParameter: Map UniqueID
FIELDLAYER_PARTICLE_SOURCE_MODE_INDEX_MAP_UNIQUEParameter: Radius
FIELDLAYER_PARTICLE_DISTANCEParameter: Value Source
FIELDLAYER_PARTICLE_SOURCECHANNEL_VALUEParameter: Color Source
FIELDLAYER_PARTICLE_SOURCECHANNEL_COLORParameter: Direction Source
FIELDLAYER_PARTICLE_SOURCECHANNEL_DIRECTIONParameter: Clip to Shape
FIELDLAYER_PARTICLE_CLIPParameter: Color Alpha
FIELDLAYER_PARTICLE_COLOR_ALPHA