As of now, ATA is not on Coinbase. ATA is an ERC20 token on the Ethereum blockchain. The project is in its early stages, and the team is currently focused on finishing the product and building partnerships. Once the product is launched and ATA gains adoption, the team plans to list on major exchanges.
So far, ATA has been listed on IDEX and ForkDelta. In the future, ATA may be listed on Coinbase, but this has not been announced yet.