That string would be stored in the tranasction that is generated.
However, it depends on the smart contract that you have installed. Maybe, some smart contract wouldn't save it.
You don't store anything in the contract storage, you only execute the contract. However, Blockchain stores the info twice:
Ledger: the Ledger stores all the transactions. The ledger is comprised of a blockchain (‘chain’) to store the immutable, sequenced record in blocks. Each node maintains a copy of the ledger.
State Database: maintains the current state. It represents the latest values for all keys ever included in the chain transaction log. Smart contract invocations execute transactions against the current state data.