Google+ team is fixing and rolling out an updated notifications flyover for the web version of Google+.
New Google+ notifications with Bell icon
This new layout looks cool with notifications clearly called out by previously read and unread notifications. Looks clean and easy to consume the notifications.
If you see a bell icon just next to the share button, then you already have the latest notifications. If it doesn’t appear automatically you may try a logout of Google+ and re-login again. Sometimes this works when tried from chrome incognito mode.
This is incrementally rolled out, so if it doesn’t still show up please be patient and it may arrive shortly for your account.