How to Enable USB debugging mode of Sony Xperia Z Ultra C6802
STEP ① - Tap on "Menu" icon of your mobile device
STEP ② - Launch the Settings app on your phone.
STEP:③ - Scroll down to reach “About Phone” option
STEP:④ - Tap on “Build number” for 7 times to go to developer option.
STEP:⑤ - Go back to "Settings".
Now, you can see developer option appear in the setting list, tab on it and allow development settings.
STEP:⑥ - Tap on USB debugging option and allow USB debugging by clicking on OK button.