If you need information on your Past Employees' training, you just need to check the Past Employees Dashboard. To do so, click on the Admin tab, select Reporting from the left-side menu, and then hit Past Employees Dashboard.
Search for the user in question, filter the users based on the deactivation date, or use the org structure filtering options. Once you find the user that you want to, click on his/her name to see some more details on his/her training.
Once you click on the name of a specific user you will have access to his/her:
4. On the Job Training tasks
6. Career Paths (if you have enabled this feature for your academy - advanced settings)
Just click on the relevant tab and you will be able to see some more information for the different types of training.