You can also try these:
if the thumb drive is partitioned:
ls /media/
(insert thumb drive)
(wait 5 seconds for the thumb drive to settle)
ls /media/
The second time it will show another mount point that wasn't there before.
If the thumb drive has no partitioning or the above didn't work:
dmesg
(note the end of the messages so you have a point of reference)
(insert thumb drive)
(wait 5 seconds for the thumb drive to settle)
dmesg
The new messages pertain to your thumb drive.
You can also scroll back (Shift-PageUp) dmesg to find the thumb drive if it was already inserted.