It is the first and only book which I purchased and have in My Library to use as a test case
When I double-click I do so on the mouse which I use to operate my desktop computer.
My problem was not solved. I was told to take steps without being told how to take them. No account was taken by the Expert of the level of my ignorance. BotXXXXX XXXXXne for me: I still have a book showing in my Kobo Library which I am unable to open. I do not wish to waste any more of the Expert's time - or mine - or my money.
When I click the sync icon in the Kobo Desktop I am notified that "Syncing Kobo Desktop" is occurring. This is followed by "Updating annotations", then "Sync Complete" and "Your latest books are in your Library". However, when I double-click the cover of the book in My Library, nothing happens, it does not open. Please bear in mind that I am an octogenarian if you really wish to pursue this matter further; I reckon that am computer-illiterate as far as you are concerned. Thank you.
As I understand you now, I need to purchase another device (a Kobo) which would operate separately from my computer - like a kindle, perhaps ? I do not have such a gadget.