The password for your Demo Account is sent to your email and is displayed during the registration process. It is also contained in a message which you can find in your MetaTrader inbox (“Terminal” — “Inbox”).
You can recover a lost or forgotten password from myAlpari in the section My Trading Accounts — “Account Overview”. Please note that you can only recover passwords for Demo Accounts which are still active.
If your Demo Account is not active, you can simply open a new one.