Closed Caption Icon does not appear

Hello Luciana, 

Thank you for your support. Matthew has already responded to me and now  I understand my problem was very easy to solve. 

I was sure if I add subtitles once, on the base layer, the CC button will appear on all of them. I didn't add the subtitles on the rest of the slides, because when I noticed there is no CC button on layers above, something is wrong. Fortunately the thing is that if you have no captions added, the CC button will not appear.

I hope it might be helpful for other new users (as I am) in the future :)

Thank you for your support!