dApps can easily read dAPIs with API3 Market proxy contracts. Use the API3 Market UI to obtain the proxy contract address for any dAPI such as AAVE/USD on the Mumbai network. A proxy contract only reads from single predefined dAPI. There are many dAPIs, each of which has its own proxy contract which in turn reads the dAPI's data (value int224, timestamp uint256).
Currently each self-funded dAPI has an on-chain proxy contract with an address that is publicly available to any dApp. For example, the proxy contract address of the dAPI AAVE/USD on the Mumbai network is 0xa8785d83A31B21065F27b640F50694b39B1bda9a. This address is used to read (via IProxy) the dAPI's data (value int224, timestamp uint256).