How do i make a script to play a sound once?

If you don't want to sound to be played locally to the player, then use a ServerScript.

local debounce = false

script.Parent.Touched:connect(function(hit1)
    if not debounce then
    debounce = true
        script.Parent.Sound:Play()
        wait(3) --how long you want before it can be touched and played again
    debounce = false
    end
end)

Let me just run through quickly on what you did wrong.

local debounce = false

script.Parent.Touched:connect(function(hit1)
    if debounce == false then
        script.Parent.Sound:Play()
        debounce = true 
    end
end)

Here, you placed debounce = true and debounce = false in the wrong place.

Btw, idk why you put hit1 in the parenthesis. Unless you're trying to identify that it's a player, I suggest that you do this:

local debounce = false

script.Parent.Touched:connect(function(hit1)
local character = hit1.Parent
    if not debounce then
    debounce = true
    if character and character:findFirstChild("Humanoid") then
        script.Parent.Sound:Play()
    end
        wait(3) --how long you want before it can be touched and played again
    debounce = false
    end
end)

What that does is that it looks for "Humanoid" in the character.

Hope this helps!

EDIT(because asked):

local debounce = false

script.Parent.Touched:connect(function(hit1)
local character = hit1.Parent
    if not debounce then
    debounce = true
    if character and character:findFirstChild("Humanoid") then
        script.Parent.Sound:Play()
    end
        wait(3) --how long you want before it can be touched and played again
    debounce = false
    end
end)

script.Parent.TouchEnded:connect(function()
    --your code
end)