I used to receive notifications when someone thumbs up my comment or replies to it on G+ but not any more. I only receive replies now even though when I go to old videos I see that my comments has some thumbs up!
At the present time, there is no setting that allows you to get notifications for upvotes (or downvotes) on comments.
The feature to which you are referring was the ability to receive a Google+ notification whenever someone +1'd a comment that you made on a YouTube video. As part of Google's undoing of YouTube's integration with Google+, which began mid-summer 2015, they switched the comment voting system back to thumbs-up/thumbs-down, removing the +1 Button. When they did this, they did not implement any system of notification for votes on your comments.
However, there is still a setting that enables you to receive email and/or push (phone) notifications for replies to your YouTube comments. To customise this, go to your Google+ settings, and make your preferred selections in the expandable "Posts" table within the "Receive notifications" section (near the top).