I put a script inside a part the script should play a song if the part was touched why wont it work?

Try This:

script.Parent.Touched:connect(function(h)
    local hum = h.Parent:FindFirstChild("Humanoid")
    if hum ~= nil then
        game.SoundService.endmusicsong:play()
        if game.SoundService.endmusicsong.IsPlaying then
            game.Workspace.endmusicpar:Destroy()
        end
    end
end)

I've changed the :Play() from Line 5 to ".IsPlaying" IsPlaying can find if the music is currently playing or not. This is the variable you are looking for!

That would be because you play it and then destroy the part right after, not allowing it to play. Also, the Play method doesn't return a boolean. I also added a debounce (for obvious reasons).

local SoundService = game:GetService("SoundService")
local debounce = false

script.Parent.Touched:Connect(function(Hit)
    if debounce then return end
    debounce = true

    if Hit.Parent:FindFirstChild("Humanoid") then
        if SoundService.endmusicsong.IsPlaying then
            script.Parent:Destroy()
        else
            SoundService.endmusicsong:Play()
        end
    end

    wait(1)
    debounce = false
end)