Why isn't this debounce working?

You actually have a couple things wrong here.

In the Touch event you have 2 if statements and only 1 end, along with the variable enabled being set to true on Line 1. Here is a cleaner and fixed version of your code.

local enabled = false

x.Touched:connect(function(Hit)
    if not enabled then
        enabled = true
        local HitPlayer = game.Players:GetPlayerFromCharacter(Hit.Parent)
        if HitPlayer and HitPlayer ~= player and Hit.Parent:FindFirstChild("Humanoid") then
            Hit.Parent.Humanoid:TakeDamage(20)
             wait(10)
            enabled = false
        end
    end
end)

The enabled value starts at true. On line 4, the conditional statement only allows the code below it fire if enabled is false. Just change enabled to false in the beginning and it will work.