Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Camera
STAGEOBJECT_CLINKParameter: Sky
STAGEOBJECT_SLINKParameter: Foreground
STAGEOBJECT_FLINKParameter: Background
STAGEOBJECT_BLINKParameter: Environment
STAGEOBJECT_ELINK