Is it possible to check when the portable hard drive was last accessed

So get yourself a spare USB drive and write some files to it and open them. Close them and eject USB.

Reboot.

Plug USB in again and check last accessed date.

Then eject and plug it into another machine. check the last access date is the same as before. Then view some files. Close them and eject. Now plug it back into the original machine and check last access date.

Anyway as already stated if it's that important, encrypt your drive, folders or files.

Create an Linux USB live stick (example Linux Mint), boot in to linux from that live stick.. attach the external drive.. Open the folder "System Volume Information" check the date of those files.. 99% of the time when you attach a external NTFS drive to a windows computer, those files will be updated.
Also open the folder Recycle.. Most often when you attach a external drive to a new computer, that computer creates a new sub-folder.

If your friend had a linux laptop it will not leave any traces as Linux dont write to disk as windows does.


Edit
Important note..
If you start playing around with disk encryption. make sure you have at lest one backup, even better with two sets of backups.. as data-recovery is almost impossible on encrypted harddrives, even if you have the password.. only a few exceptions is making that rule of the impossible..

You should always have backups.. but it becomes even more important to have that if you use encryption solutions...

Just have a look on this forum on people that have lost there beloved family photos and stuff do to data-recovery didn't work and they had no backups.