Windows 10 New Snip & Sketch Tool notification missing

Might be it is disabled, Try below method.

Go to Local Group Policy Editor. If you cant make that out than go to run and write this command - gpedit.msc to open local group policy editor.

In the left pane - -> User Configuration - -> Administrative Template -- > Start Menu and Taskbar - -> in the side panel find - "Remove Notification and Action Center". - -> Double Click on that - -> if it is enabled then make it disabled. Restart your PC.

Might you get the solution.

Source taken from : http://www.tenforums.com/tutorials/6004-action-center-enable-disable-windows-10-a.html

OR

you can do something like this :

Start Menu - - > Setting - -> System - -> Notification and actions - -> Turn system icon on or off. - -> Action Center - -> if it is off - -> On it.

I'm asking about why the notification "toasts" (again, I don't know the Windows terminology) are never making it into the Action Center in the first place.

The toast notifications are transient by definition, so they vanish after a bit of time, unless they require action.

From MS:

"A toast notification is a transient message to the user that contains relevant, time-sensitive information and provides quick access to related content in an app."

It's up to the app's developers to pick the notification type. Since the Action Center is an extension of the toast notification system that existed in Windows previously (since like XP), notifications triggered using old APIs/methods will act like they used to, which includes not being added to the Action Center list.

You can control how long transient toast notifications stay visible via Settings -> Ease of Access -> Other options -> Show notifications for, where you can set them to last onscreen for up to 5 minutes.