First, don’t use the device node names directly; there is no guarantee that they are persistent across restarts, so you might be looking at a different device, when you reboot and pull that command from the history and repeat it.
The real problem seems to be that you directed fdisk to the first partition on your device and it seems to find another (nested) partition table, or at least misinterprets what’s there.
Run it like this:
sudo fdisk -l /dev/sda
(NO number at the end)
As for your space problem and the “moving to trash” taking actual I/O time, that’s most probably caused by the Trash folder residing on your $HOME, which is probably close to bursting. Usually, you shouldn’t need to move things to trash, just delete files and Dolphin will move them to the local trash folder on the corresponding device, which is an almost instant action, because no data is actually moved around; just some bookkeeping to link them to the trash folder and then unlink them from where you deleted them.
You should keep an eye out for the actual confirmation dialog and what it says. I’m not a KDE and thus not a Dolphin user, but I am fairly certain that it will warn you if it can’t move things to trash which would make your deletion irrevocable; in GNOME Files the button turns red in that case and the message says “permanently delete?”.
Moving data from the external device to your $HOME’s trash does require copying it first, hence the delay and your out of space warning.
Why didn’t you click on “Show Details…”? 
I bet that this will reveal the cause of the “out of space message”:
df -h "$HOME"
And are you aware that action is irrevocable? 
There is no detour to the Trash purgatory, so no way of restoring files, which is the purpose of Trash to begin with.
Usually one can circumvent the Trash by pressing ShiftDel in the desktop file manager, if that’s what is actually desired.
Please put all log and other console/terminal output in pre-formatted code blocks (open a new line, click the </> icon in the editor first and paste into the new element), ideally wrapped in a “Hide Details” element, if it’s more than just a few lines. See items 4 and 5 in the Posting Guide.
Optional helper script
If you are so inclined, I took it upon myself to provide a little helper script for that. 