Forensically speaking, the most interesting tidbits of information when it comes to Cortana can be found in the following location: C:Users[User]AppDataLocalPackagesMicrosoft.Windows.Cortana_xxxxLocalStateESEDatabase_CortanaCoreInstanceCortanaCoreDb.dat

Here you will be able to uncover information such as the locations the user has been in, the reminders they have set, where and when those reminders were triggered, and where and when the reminders were marked as complete.

This can be of particular interest if your case hinges on putting someone in a certain place at a certain time. Likewise, a reminder that has not been marked as complete may demonstrate that the users plans changed at the last minute.