how to check a specific part touches another part?

To do this you need to add what is called an if statement. An if statement checks whether an argument is true or false.

Here is what you would do:

local part = script.Parent
local part2 = script.Parent.Parent.Specificpart

local function onTouch(part)
    print("Touch started: " .. part.Name)
     if part == part2 then print("Part is the same") end
    part2.Size = Vector3.new(4,4,4)
end

local function onTouchEnded(part)
    print("Touch ended: " .. part.Name)
    part2.Size = Vector3.new(1,4,1)
end

part.Touched:Connect(onTouch)
part.TouchEnded:Connect(onTouchEnded)

You can get the hitted part's name:

script.Parent.Touched:Connect(function(hit)
    if hit.Name == "Part2" then
        hit.Size = Vector3.new(4,4,4)
    end
end)

script.Parent.TouchEnded:Connect(function(hit)
    if hit.Name == "Part2" then
        hit.Size = Vector3.new(1,4,1)
    end
end)

Hope this helped!