Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Time
TLMARKER_TIMEParameter: Length
TLMARKER_LENGTHParameter: Color
TLMARKER_COLORParameter: Task
TLMARKER_TASKParameter: Done
TLMARKER_DONEParameter: Export as Animation Take
TLMARKER_EXPORT_ANIMATION_TAKEParameter: Note
TLMARKER_TEXT