I know ETH fork new coin and I want to know how ETH prices change. And Should i buy ETH this moment?
There will be no new coin from ethereum fork, remember the latest fork of ethereum doesn't generate a new coin. You should search the latest news about that. It seems like you have been missing it. as far as i know this update will focus to improve the protocol in ethereum platfotm. It's not about issued a new token.
People always assume a fork will bring out a new coin. I have also had this understanding before the last fork, when I had to meet a guru to actually explain what fork is all about. Many will claim to know while in essence they are novice in most things. We learn everyday.