I've never done this myself and do not recommend it. I used to work for Amazon and was very involved in the Kindle department. It is very easy to mess up 'jailbreaking' a kindle and turning it into a useless brick. If that happens, Amazon will show no pity on you and they will not repair, replace, or even assist you with the device in any capacity. It voids the warranty completely. I had more than one call from someone attempting to do this with their pretty, shiny, $300+, new Kindle HDX and having to tell them that they will just need to get a new device.
Kindles cannot read Nook books and Nooks cannot read Kindle books. It's sad, but that's how the devices are programmed.
If you want to try to jailbreak it, just do so knowing that it can turn the device into a pretty paperweight.
You're better off trying to download the Nook reader from Google Play and attempting to sideload it onto the Kindle. At least Amazon can help you factory reset or remove it if it doesn't work. Most Google Play apps will work on the device, but you have to sideload it. Warning though, I worked primarily with the Fire devices. I don't know much about the Paperwhites, so I'm not entirely sure if you can even put apps on it.
Good luck with whatever you end up trying.