Apple or iOS Mobile Devices
Tap the video to make the player controls appear, then tap CC in the lower right corner to toggle closed captioning on and off.

You can manage captions further in Settings on your iOS device. Tap General > Accessibility > Subtitles and Captioning for more options.  

Android Mobile Devices
Tap the video to make the player controls appear, then tap CC in the lower right corner to go to Google Subtitles (CC) in Settings. Tap the switch from Off to On.

You can also manage the text size and style, then return to the Nick App to continue watching with subtitles.

Android TV
Closed captions are controlled from the accessibility menu of your Android TV device. Use your device's settings menu to access the functionality.

Alternatively, you can access the accessibility menu from full episodes in the Nick App, by using the CC button in the upper right of the video playback screen.

Roku
  1. In the channel, press the asterisk (*) button on your remote, and go to Settings.
  2. In Settings, press the Closed Captions button to toggle closed captions on and off.
Alternatively, you can simply press the asterisk (*) button on your remote while you're playing a video to enable or disable closed captions.

Fire TV
Closed captions are controlled from the accessibility menu of your Fire TV device. Use your device's settings menu to access the functionality. Follow these three easy steps:
  1. Press "Home" on your Fire TV remote
  2. Select "Settings" > "Accessibility" > "Closed Caption"
  3. Select "Closed Caption OFF" or switch to "Closed Caption ON"
  4. Press the "Home" button and re-select the Nick app to continue watching
If you don't see captions, or if you're having trouble getting them to work, feel free to submit your comments or concerns here: http://media.viacom.com/accessibility/