I am from Pakistan where Kindle is not available so i wonder it would work or not if I buy Kindle
Depends on how you want to use it.
The device itself has no VPN settings so if anything you would need to let your network run truth the vpn and not only one device.
But you can still easily work with side loaded books so you would not need to buy book from amazon.
In this case, to be fair, other ebook readers which are not highly tied to a vendor ecosystem with the sole purpose to sell digital content, might be easier for you in the long run.
The Kindle itself will work wherever you are. It depends on the amazon store you use.
Kindle is just the device. You buy the ebooks from the website. You can try it now yourself if you want.
You would just need to link it to an amazon / audible account with a UK address - if you have any friends / family in the UK whose address you could use - or just find a random one online.
You can buy a Kindle device though VPN, if you find a way to deliver to your place (not only Amazon sells Kindles, here even Media Markt does it). The device has no VPN functionality, it used the WiFi’s capability it connects to (meaning if you tether a network that is connected to a VPN then Kindle will also communicate through the VPN tunnel). But you can use the reader without internet connection.
One of the best things of owning a Kindle reader is the access to thousands of free ebooks on Amazon.com. There’s no end of reading material.
I have my family in UK