If you use iTunes U in order to view and listen to courses, you may have noticed that some of those courses have support for closed captioning. For users with disabilities, iTunes U also allows you to turn on closed captioning by default so whenever it's supported, it will use it.
Launch the Settings app from the Home screen of your iPhone or iPad.
Scroll down and tap on iTunes U
Turn On the option for closed captioning.
iTunes U will now obey that setting and implement closed captioning for any lessons or courses that support it.