There's a couple things you need to do to get the effect you desire.
The first thing you need to do is create your window object in your menu scene.
Find the main method in your menu scene, it looks like this:
CODE
def main
s1 = $data_system.words.item
s2 = $data_system.words.skill
s3 = $data_system.words.equip
s4 = "Status"
s5 = "Memory"
s6 = "Quicksave"
s7 = "Quit"
#ect.
Anywhere under the word main you need to create the window like so.
Also you should set window visibility to false so you can't see it when you open the menu.
CODE
@confirmation_window = Window_Confirmation.new
@confirmation_window.visible = false
The main method should look something like this:
CODE
def main
#create the confirmation window
@confirmation_window = Window_Confirmation.new
@confirmation_window.visible = false
s1 = $data_system.words.item
s2 = $data_system.words.skill
s3 = $data_system.words.equip
s4 = "Status"
s5 = "Memory"
s6 = "Quicksave"
s7 = "Quit"
#ect.
Then you need to find where you want to activate the window which I'm guessing is here:
CODE
when 5
#Play Decision SE
$game_system.se_play($data_system.decision_se)
# Quicksave Game
$game_system.map_quicksave
delay(0.5)
#Return to Title Screen
$scene = Scene_Title.new
Instead of sending you back to scene title straight away we are going to show the window so it should look something like this
CODE
when 5
#Play Decision SE
$game_system.se_play($data_system.decision_se)
# Quicksave Game
$game_system.map_quicksave
#show the confirmation window
@confirmation_window.visible = true
After this we want it to check for your button input to send you back to the title, but we only want it to check for this said input when the window is showing. To do this we find the update section:
CODE
def update
@command_window.update
@status_window.update
@map.update
#ect.
and we're going to put in the check for your button input to exit to the title screen when the window is visible.
CODE
def update
#if the confirmation window is visible
if @confirmation_window.visible
#if the input key is either C or X
if Input.trigger?(Input::C) || if Input.trigger?(Input::B)
#Play Decision SE
$game_system.se_play($data_system.decision_se)
#hide the confirmation window
@confirmation_window.visible = false
#exit to title scene
$scene = Scene_Title.new
end
#cancel the rest of the update method
return
end
@command_window.update
@status_window.update
@map.update
#ect.
Ok and finally we need to dispose the confirmation window to free it from the memory. Even though its not visible, it doesn't mean its not there. We dispose windows at the end of the main method. Find this section:
CODE
Graphics.freeze
@command_window.dispose
@game_stats_window.dispose
@status_window.dispose
@map.dispose
end
Now we are going to add the confirmation window to the list of other disposed windows.
CODE
Graphics.freeze
@command_window.dispose
@game_stats_window.dispose
@status_window.dispose
@map.dispose
#dispose the confirmation window aswell
@confirmation_window.dispose
end
And that should be it. I did this all from memory and haven't tested it at all because it's late and I'm tired

I may have forgotten something or I may have made a stupid spelling mistake so if it doesn't work or you can't figure it out I'll fix it tomorrow.