Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Time
TLMARKER_TIME
Parameter: Length
TLMARKER_LENGTH
Parameter: Color
TLMARKER_COLOR
Parameter: Task
TLMARKER_TASK
Parameter: Done
TLMARKER_DONE
Parameter: Export as Animation Take
TLMARKER_EXPORT_ANIMATION_TAKE
Parameter: Note
TLMARKER_TEXT