Can I connect my laptop and PC?

So you can use his older laptop as a second screen? If yes how? Where do you have to connect this?

If the laptop is used as a terminal, that certainly works.

For this you need a terminal software, but I do not know that.

Just like that cable from the PC does not work, because laptops usually have no input to use the display as a monitor for external devices. Is still software where you send the PC signal over the network to the laptop, but has just bad latency!

In short: buy your second monitor!

Is complicated, a used simple screen costs 5-40 euro so you save the work.