List

Clicking Notifications in the sidebar brings up a list of past and current notifications:

Notifications that haven't been acknowledged will be displayed in bold and have a check icon you can click to acknowledge them:

You can also Acknowledge All notifications, or Acknowledge Visible notifications (everything you can currently see on the screen) by clicking these buttons:

If you turn on the Show Acknowledged switch, it will also show past notifications that you have acknowledged:

You can access more options for filtering which notifications to view by expanding the More Filters section:

This section allows you to see All Notifications (those sent to other users) if you are an admin, and filter notifications by Device or Group and a time range: