In case someone doesn't know, here is how monitors work.
Devices have output ports, let's call it port A
Monitor have input ports, Let's call it port B
You plug stuff in from port A to Port B. Output, sends image/video information for input to receive. That is how it works, changing it requires some expert technical skill to actually modify said devices to do such things. Laptop only has one input and is the system itself, but as someone already said, you can use a capture card like Elgato gaming HD, or Avermedia, those are also inputs but also outputs at the same time. So that is a option, of course is not the best. Using tools like that, it has delay on PC cause it actually process videos on the fly to display on the computer.