The account ID is your unique 28 character ID. It is a reference to where all your created data should be stored in the server - it personally identifies you and where all your data is stored.
In order to help look into bugs and solve problems on your account, your Social Dummy account ID will be required. This helps to try to reproduce issues that you've come across and resolve your issue much faster.
Locating Your ID
Open the side menu
Tap your avatar.
Tap "Account ID" to copy the unique string.