I assume this is a USB mass storage key, when plugin the key you should see the usb device detection with dmesg:
[ 44.162311] usb 1-1.2: new high-speed USB device number 4 using xhci-hcd
[ 44.287536] usb-storage 1-1.2:1.0: USB Mass Storage device detected
[ 44.296592] scsi host1: usb-storage 1-1.2:1.0
[ 45.355785] sde: sde1
This means your USB key has been correctly enumerated and device present into /dev directory. You should then be able to mount one of the partitions (eg. sde1) and access the files.
$ mount /dev/sde1 /media