In the Windows 10 Action Center – lower right of the screen, you may get what are called Toast Notifications from applications like Microsoft Outlook and other programs on your computer. These notifications are stored in a database and can be seen by clicking the icon in the lower right of your screen. The entries that are there are held for a period of time, until the expire at which time they are purged from the database. As long as the entry is in the database it can be seen in the Notification portion of the Action Center.
If you want to access this database it is located in %localappdata%\Microsoft\Windows\Notifications\wpndatabase.db the database is SQLite database you can open that file with DB Browser for SQLite. Each user has their own database for Notifications.
In the Notifications table you will find all of the entries that have not expired out of the database and can use the Browse Data tab to look through the Notification table using DB Browser for SQLite.