You can view cancelled appointments within the appointment book by following the below steps:
Select your name at the top right-hand corner > 'user settings'. See below:
Under the 'Appointment Book' tab select the checkbox beside 'show cancelled & deleted appointments'
Any appointments will then appear in black on the appointment book if they have been cancelled or deleted.
Alternatively, you can run the 'Appointment Report' under the 'Reports' section > 'Appointment' > 'Appointment Report'. This will display all appointments. This report can then be filtered by 'appointment status to display only cancelled appointments.