how to run animation on ClickDetector click?

Since animations can be played back on the client and be replicated to the server, and the client can access a click detector's input events, there isn't a solid reason to use a server script. So you can ditch the server script and just use a local script

--this should be a local script
local plr = game.Players.LocalPlayer

function click (plrClick)
    if plrClick and plr then
        if plrClick == plr then
            hum = plr.Character:FindFirstChild("Humanoid")
            if hum then 
                anim_feet = hum:LoadAnimation(workspace.Part.Animation)--or wherever your animation is located 
                current = anim_feet-- i don't see why this is necessary  
                current:Play() 
                wait(2.5)
                current:Stop()
            end
        end
    end
end
workspace.Part.ClickDetector.MouseClick:Connect(click)

this should be a local script in (preferrably) starter character scripts, this establishes the local player, then when the click detector is clicked, it checks if the player who clicked the thing is the local player, then if it is,it checks if there is a humanoid, if som then it plays the animation

And if there is anything wrong with this, just let me know

You can't use the variable LocalPlayer in a normal script.

heres the fixed script:

function onClicked(hit) 
if hit.Parent:FindFirstChild("Humanoid") then
plr = game.Players:GetPlayerFromCharacter(hit.Parent)
hum = plr.Character.Humanoid 
anim_feet = hum:LoadAnimation(script.Parent.Animation) 
current = anim_feet 
current:Play() 
wait(2.5)
 current:Stop() 
end 
end
script.Parent.ClickDetector.MouseClick:connect(onClicked)