You can look up the canister smart contract identifier for any specific canister that you've deployed on the Internet Computer by running the dfx canister id command.
For example, to look up the the canister identifier for the lookup canister deployed on the local network, you can run the following command:
dfx canister id lookup
To view in-depth information about looking up canister identifiers after deployment, please check out the Look up a Canister ID section on the Internet Computer Docs.
More information on canisters can be found here.