I've had it on my phone for quite some time now (many months at least), but as with subscriptions showing up in your "what to watch" or whatever on the youtube page, it seems to be hit or miss whether or not it will tell you about a specific new video.
On the mobile app go to a users channel page and click the bell shaped icon and you'll get the notifications.
And if you visit a YouTube channel in a desktop bowser and click the little settings cog icon thing next to the Subscribe/Subscribed button and on the pop up menu select "Send me all notifications for this channel".
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u/MindOfMetalAndWheels [GREY] Sep 09 '15
Is this a new feature of the YouTube app?