Please check the FAQ in the document package (document tab, for latest JB: https://www.freescale.com/webapp/Download?colCode=IMX6_JB422_110_ANDROID_DOCS&location=null&fpsp=1&P...) , USB debugging is part of developper settings menu :
27 How do I enable developer settings on Android 4.2?
Google has hidden the developer settings in the latest version of Jelly Bean. The following steps explain how to retrieve developer settings:
• Go to the settings menu and scroll down to "About phone." Tap it.
• Scroll down to the bottom again until you see "Build number."
• Tap it seven (7) times. After the third tap, you'll see a playful dialog that says you're four taps away from being a
• Keep on tapping, until you've got the developer settings back.