Oh, you actually have a few drives plugged in so that makes it more tricky to identify based only on this (although it also highlights the importance of double checking, especially if you plug/unplug drives frequently).
But I'm seeing now from your first screenshot that Disks also has this right at the top, under the window title. In the screenshot, this drive is listed as /dev/sdg but, again, this may change as you plug/unplug drives so double check.
The number of drives does not matter, nor does which physical connections or ports were used. Linux registers drives similar to Windows, only using a different naming scheme; each drive receives a designation as the kernel recognizes it, in order. This means that the same USB drive plugged on the same USB port may receive a different designation between reboots.
But anyway, it's probably much easier to just open Disks and select the drive you're interested in, and use whatever designation its shown for it at the top of the window. Then, use that to follow Aravisian's advice to mount, unmount and run a file system check on it, and see what comes out of it.
I'd like to thank you all for your help but I'm going to give up on this. As usual your splendid advice was helpful and informative, albeit beyond my understanding.
Thanks again.
