Well in the "Settings", "Apps" area of the device, there should be sections for "Downloaded" ones. So any app you downloaded and installed yourself would be there. However, considering how tricky some people can be, it is possible an app can be placed on the device and not show in that list. The only way I know of to make sure there is absolutely nothing on the device would be to first save all your personal data (contacts, photos, videos, music, etc., not apps) to a cloud account or computer and then do a "Hard Reset" of the device. This will wipe all data off the device and reinstall only the original OS and apps.
NOTE: Doing this will clear 'all' the data on your phone, so it is suggested you not choose this option unless you have...