macOS keyboard shortcut to dismiss notifications?
You can create Automator service to run this Applescript and give it a keyboard shortcut in the System Preferences Keyboard shortcuts

This will close Alert and banners Notification



In Automator choose a new service





Add a Run Applescript Action 





and replace it's code with:

my closeNotif()
on closeNotif()

    tell application "System Events"
        tell process "Notification Center"
            set theWindows to every window
            repeat with i from 1 to number of items in theWindows
                set this_item to item i of theWindows
                try
                    click button 1 of this_item
                on error

                    my closeNotif()
                end try
            end repeat
        end tell
    end tell

end closeNotif




Set the 'Service receives [no input] in [any application]'

Save the service.



Open the Keyboard shortcuts in System prefs and set your for your service under 'Services'


Now any newly launched app will pick the shortcut up.

(Note: I structured the script to counter throwing an error that will occur when the notifications/windows start to close.

otifications/window are numbered 1 through to the total count. But as they close the script would still be working of the old count. 
But the system will be re assigning the index of the windows.

So where we say start at 1 -6 the script will try and close window 1, window 2, window 3 and so on. But the system has re assigned the window numbers 1,2,3 to the last remaining windows. But the script will try and close window 4 and throw an error because it does not exist. The script will catch this and deal with it. )



If you want to click the 'Show' button on an Alert Notification.
you change the button you click from 1 to 2.

click button 2 of this_item


Banner notifications do not have a button 2.

But you can just click the window.

So this code should take care of Showing.

my closeNotif()
on closeNotif()

    tell application "System Events"
        tell process "Notification Center"
            set theWindows to every window
            repeat with i from 1 to number of items in theWindows
                set this_item to item i of theWindows
                set cnt to count buttons of this_item
                try
                    if cnt &gt; 1 then

                        click button 2 of this_item
                    else
                        click this_item
                    end if
                on error

                    closeNotif()
                end try
            end repeat
        end tell
    end tell

end closeNotif