I want to create an API endpoint that displays only Total Supply as a numerical value in CryptoID like this, http://chainz.cryptoid.info/grs/api.dws?q=totalcoins I don't know where to start this is why I didn't commit any code for this. I have seen a lot question like this but no exact answer.
You should start with something like how to get coin total supply…
For ether for instance, you would use web3 provider to call smart contract that is token and check coins left. Or use etherscan api.
Then you can write some service that would take contact addresses and update some sort of database… so you can use that database as data provider for your api…