"zagar" means "a tan" in Russian, so this sentence sounds funny.
Nie pomniu etogo zagara. I don't remember this tan. ŁÓŁ
No. It would be visible in Accusative - a positive sentence "I remember this clock" will be "Pamiętam ten zegar" as "zegar" is masculine but not animate, and thus its Accusative = Nominative.
But here it changes to Genitive because of negation, so it's not visible whether it was animate or not.
Oh gosh you're right, this negation genitive thing keeps catching me out, time and time again.