A transaction hash/id is a unique string of characters that is given to every transaction, which is verified and added to the blockchain. In many cases, a transaction hash is needed in order to locate funds.
In Cake Wallet, you can find a Transaction ID on the Transaction Details screen.
Swipe right to left from the main balance screen to find the transaction history. Tap on a transaction and you will see the Transaction Details screen. The Transaction ID will be at the very top.