Why is there an alarm clock badge on the YouTube app?
The icon is telling you why Siri is suggesting the app to you by placing it in the Dock. Siri's proactive abilities means it suggests apps it thinks you are likely to use for a variety of reasons:


Alarm icon: app suggested because of the time of day
‘Location’ arrow: app suggested because of your current location


You can disable apps from being suggested on the Dock by going to Settings → General → Multitasking &amp; Dock and disabling Show Suggested and Recent Apps.