Click on the Green Bell at the top right of the screen to open the Notifications pane.

Notifications will be displayed with a solid orange dot to the right, to mark as read hover your mouse over this dot, the hover message will display, Mark as read, click the dot so that it becomes an orange circle

You can Manage and Filter the Notifications as required using the options in the Notifications pane, additionally the Overflow Menu allows for Bulk Updates of Notifications.