UserInputService. Is my syntax broken?

So, the problem is, you are trying to access ServerScriptService in a LocalScript, however LocalScripts, cannot access server only instances, hence the names containing "Server", try storing your leaderstats in ReplicatedStorage, where both the client and the server can retrieve data.

I think the problem is that on the 2nd script (line 6), you inserted something named "leaderstats" into the player, but in the 1st script at line 7, you got that "leaderstats" in the ServerScriptService. Also, you inserted in that leaderstats a IntValue named "Pow", but in the 1st script you wrote "leaderstats.Power", although it was named "Pow".

There is another error. In the 15th line in the 1st script, you added 1 to the value of "Pow". But you wrote this in a local script. So it will not change the value of "Pow". To do this, you have to send a signal from that localscript to a normal script with a remote event. Insert a remoteEvent in ReplictedStorage (name it whatever you want) and insert a normal script into Workspace.

So you can replace your 1st script by this:

repeat 
    wait() 
until game.Players.LocalPlayer.Character

local player = game.Players.LocalPlayer
local userinputservice = game:GetService("UserInputService")
local char = player.Character
local leaderstats = player.leaderstats

userinputservice.InputBegan:Connect(function(input)
    if input.KeyCode == Enum.KeyCode.E then
           local anim = Instance.new("Animation")
           anim.AnimationId = "rbxassetid://04480814830"
           local PlayAnim = char.Humanoid:LoadAnimation(anim)
           PlayAnim:Play()
           game.ReplicatedStorage:WaitForChild(WHATEVER YOU NAMED THE REMOTE EVENT):FireServer() -- gives a signal
           wait(3)
    end
end)

Then, in the normal script you inserted in Workspace, write this:

game.ReplicatedStorage:WaitForChild(WHATEVER YOU NAMED THE REMOTE EVENT).OnServerEvent:Connect(function(player) -- gets the signal and the player
    player.leaderstats.Pow = player.leaderstats.Pow +1
end)

You don't need to make any changes in the script in the ServerScriptService.

Just to make sure, in the local script (1st script), I don't know why you added a wait(3) at the end of it. If you want to let the player click "e" again before the animation finishes, you have to add a debounce. Replace that 1st script I wrote earlier by this:

repeat 
    wait() 
until game.Players.LocalPlayer.Character

local player = game.Players.LocalPlayer
local userinputservice = game:GetService("UserInputService")
local char = player.Character
local leaderstats = player.leaderstats
local debounce = false

userinputservice.InputBegan:Connect(function(input)
    if input.KeyCode == Enum.KeyCode.E then
        if debounce == false then -- checks if debounce is false
            debounce = true
            local anim = Instance.new("Animation")
                anim.AnimationId = "rbxassetid://04480814830"
                local PlayAnim = char.Humanoid:LoadAnimation(anim)
                PlayAnim:Play()
                game.ReplicatedStorage:WaitForChild(WHATEVER YOU NAMED THE REMOTE EVENT):FireServer() -- gives a signal
                wait(3)
            debounce = false -- setting it to false after 3 seconds to let the animation to finish
        end
    end
end)

Hope this helped!