How to download ABI from Etherscan
If you are lucky, you can get the ABI you are looking for from Etherscan.
- Find the contract page on etherscan.io
- Go to the Contract tab.
- Scroll down and find the API. Copy paste or export.
The ABI must be provided by the contract deployer, and cannot be (effectively) derived from just the address or the code at the address. (link)