I created my first contract erc20, implement a mint function, the case is, if I copy the code json, I paste it in another wallet I can use the interface of the contract equally, although this is not the address that created the contract. So my question, if we could get the json of any token could we have access to its interface? Is it safe that nobody can access the json except the address that created the contract?
I think you're referring to the Json ABI, the Application Binary Interface.
It's not a security risk. It merely enumerates the functions and arguments coded in the contract. This informs software clients about the structure of the function interfaces. While it is not impossible to interact with a smart contract without the ABI, all courteous developers publish it. Knowledge of the source code is sufficient to derive the ABI. It's a compiler output along with the bytecode.
Knowledge of the contract interface helps generic user interfaces such as wallets present human-readable forms. This is how etherscan.io constucts their read contract and write to contract tabs (if the source, and therefore ABI is verified.).
Knowledge of the ABI doesn't elevate user privileges in any way. They still have to sign with their own accounts.
Hope it helps.