RemoteEvent Communication

your communication between the client and server is very unsecure as some exploiter can just loop through every player and kill them like this:

for _,v in pairs(game.Players:GetPlayers()) do
    game.ReplicatedStorage.RemoteEventz.AttackToolE:FireServer(-9999999999,v.Character.HumanoidRootPart)
end

and they'd pretty much just ruin the entire server. You could just do all of this on the client, since it replicates to every client when you use :TakeDamage() on a player. Also why your script didnt work is because you did and Debounce == true then though your boolean is set to false without any line setting it to true before the if statement.

LocalScript

--client script 

local Debounce = false
local player = game.Players.LocalPlayer

script.Parent.blade.Touched:Connect(function(h)
    if h.Parent:FindFirstChildOfClass("Humanoid") and hit.Parent ~= player.Character and Debounce == false then
        Debounce = true
        local enemy = h.Parent.Humanoid

        enemy:TakeDamage(15)
        wait(1.5)
        Debounce = false
    end
end)

Your issue is your debounce in the server script.

wait()

Debounce = false

    game.ReplicatedStorage.RemoteEventz.AttackToolE.OnServerEvent:Connect(function(plr, Damage, Target)
if Target.Parent:FindFirstChild('Humanoid') and Target.Parent.Name ~= plr.Name and Debounce == true then
        Debounce = false
        local enemy = Target.Parent.Humanoid
        enemy:TakeDamage(Damage)
        wait(1.5)
        Debounce = true
    end
end)

The debounce is first defined as false. However, you check if the debounce is ever true Debounce == true. The debounce never changes to true, hence why the damage never gets taken by another player.