—“It’s worth distinguishing between the knowledge of a referrer and the existence of its referent. We clearly know of the referrer (concept) we call ‘unicorn’, and might someday be able to bring some approximation of a unicorn into existence as a referent. The referent of the referrer ‘unicorn’ is not real, meaning it does not exist insofar as there isn’t a thing you can point to in the world and say ‘this is what I mean’.”–Trent Fowler

Knowledge(know,knowing) is a verb – an action – not a noun (thing). Knowledge exists as long as a living mind exists to hold it, or a record of knowledge exists that is reconstructable into knowledge (experience), just as running exists only while a person runs.

Knowledge of a unicorn exists, and we label such knowledge a ‘concept’ which means some category or other of referrer. Knowledge of concepts exists, but concepts do not. Knowledge of unicorns exists, but unicorns do not.
Horses exist.
Dinosaurs did exist, but other than their descendants: reptiles and birds do not.