This is an issue of copyright and something legal, partially linked to my previous question.
But I'm really curious about this.
This is not if I should put copyright on codes from Ethereum,
It's about if I should put my used source code 'open' to people if it is based on Ethereum.
Thank you.
Depends on the licence they use.
If you mean just open sourcing your code in general, then probably. But it depends on what it is.
If it's just code/contracts on the blockchain then I'd imagine it's naturally open and public just because of how that works.