Is it possible to use a MacBook Pro as a second monitor for my iMac? Both of them have a Thunderbolt port.
If not, is there any other way?
You can not use your MacBook Pro as a second monitor for your iMac without additional software.
ScreenRecycler claims to allow you to expand your desktop across multiple computers.
Apple Target Display (Thunderbolt method)
Check this link before: https://support.apple.com/en-us/HT204592