Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Camera
STAGEOBJECT_CLINK
Parameter: Sky
STAGEOBJECT_SLINK
Parameter: Foreground
STAGEOBJECT_FLINK
Parameter: Background
STAGEOBJECT_BLINK
Parameter: Environment
STAGEOBJECT_ELINK