Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Target Group
FP_SWITCHGROUP_LINKParameter: Create Group
FP_SWITCHGROUP_CREATEParameter: Previous Group
FP_SWITCHGROUP_OUTPUT_PREVIOUSGROUPParameter: FP_SWITCHGROUP_OUTPUT_PREVIOUSGROUP_ATTRIBUTE_NAME
FP_SWITCHGROUP_OUTPUT_PREVIOUSGROUP_ATTRIBUTE_NAMEParameter: Create
FP_SWITCHGROUP_OUTPUT_PREVIOUSGROUP_ATTRIBUTE_CREATE