The iPhone 8 will ship with iOS 11 when it is officially released. Unfortunately at this time there is no jailbreak tool available for this version of Apple's software. This means there is no way to jailbreak the iPhone 8.
Jailbreaking has become less popular now that Apple has implemented many of the popular tweaks created by the jailbreaking community. However, the new iPhone 8 with all its new features may inspire someone to release a new jailbreak tool for Apple's next-generation devices.