Looking at the two screenshots. The first you have used the wrong command so you don't get the correct result. You need to type SLMGR /DLV (I've typed in upper case so you can see the correct letters)
The fact there is no embedded licence key means it did not come pre-installed from the manufacturer with Windows 10, or for that matter Windows 8. It could have been Windows 7, is there a licence label for Windows 7 on the underside of the device.
As per another post you could have Enterprise edition, which is wrong for a single user. You should ask the shop about the Windows 10 licence, but you can go with the info from here if you run the command above. Please see if you can run the command and post the screenshot so we can give you feedback. You need to be aware though that the seller may have installed an illegal licence or you need to buy a licence depending on the edition of Windows 10 installed.