Hi Rolaine
I think there are different things being asked here.
Can you confirm which page type you are using?
What is on the page with the narrative? An image and text, a video or something else?
When you say 'closed captioning', it sounds to me like something you would get if you upload a video to Youtube and the automatic CC appears that a user can toggle on or off. I don't believe this feature is automatic on a page type in Xerte.
The Synched Video page type and the Media Lesson are the only ones I can think of where you can make text appear at a set point with a video, but there is no feature to 'toggle on/off'.