You are thinking of CBNK2 (https://www.speedrun.com/cbnk2) and not CNK2 (I know, the titles are super similar, it's dumb).
Unfortunately though, in order to play CBNK2 these days you'll require a jailbroken iOS device (e.g. an old iPhone, preferably running iOS 6 or lower to avoid compatibility issues with the game) and then install the game through the means of an .ipa file. I'm not sure how to feel about linking that file on this site though so if you're still interested, drop me a message on Discord and I'll help you out.
I've recently gone through the whole process with an iPhone 3GS so it's certainly possible to get access to the game.
Alternatively you can just be lucky and have an old device that still has the game downloaded but that's not too likely.