As a metadirectory historian, me and my fellow metadirectory historians (Ahmad and James) took a look at the preview for Microsoft Azure AD Sync, and so went to take a look at the database.
Upon installing the preview we opened up SQL Management Studio but to our chagrin were unable to find the Sync Database. Ahmad was delighted to find (or not find) that the product was locked down such that the database was invisible. A quick look at the running services (Get-Service *sql*) revealed two running SQL instances (default, and SharePoint). A quick look at Task Manager revealed three running SQL instances, and one without an associated service (our suspect). A quick Bing search revealed that SQL Express acts this way, and the connection string should be in the format of (localdb)\<instance name>. The Sync registry settings showed us the instance name, so the connection string should be: (localdb)\WindowsAzureActiveDirectorySyncDatabase
In the end we were able to use SQL Management Studio to connect to (localdb)\WindowsAzureActiveDirectorySyncDatabase, and begin poking around the new database.
Hopefully this post helps you find the database quicker than we did!