I think the token proof program for confidential transfers is not yet deployed to mainnet. It will come with Solana version 1.18.x.  

https://github.com/anza-xyz/agave/wiki/v1.18-Release-Schedule


They may be already on devnet. Not sure. But you can for sure run them locally already: 

1. Clone the token extensions repo: https://github.com/solana-labs/solana-program-library/tree/master/token/program-2022
2. run cargo build-sbf to build the program
3. start the test validator solana-test-validator --bpf-program TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb path/to/your/solana-program-library/target/deploy/spl_token_2022.so
4. cargo install --version 3.4.0 spl-token-cli ; this install the binary to ~/.cargo/bin/spl-token for me
5. run spl-token --version ; if this still gives 3.3.0, then the path to spl-token command is set to spl-token binary that comes with the solana-install package. You can verify this by running which spl-token.
6. If step 2 gives 3.4.0, then you should be able to run the confidential transfers no problem. If it gives 3.3.0, then you can update the path (temporarily if you like) so that ~/.cargo/bin/spl-token takes precedence over the solana release active package (for me it is ~/.local/share/solana/install/active_release/bin/spl-token).