It’s is not necessarily incorrect to use words that are usually uncountable in countable ways. It depends on whether there is another meaning that is countable.
Sugar can be countable when speaking of different types of sugar: three related but different sugars are glucose, fructose, and galactose. Note that even in this case, it may be more common (but not more correct) to use a construction that uses the uncountable form: “Three types of sugar are…”.
(Different types of a thing is the most common reason to see a normally uncountable noun used as a countable noun. The most familiar example might danger: though danger is usually uncountable and comes in degrees rather than discrete quantities, we can also say that “dangers abound”, to say that there are many types or sources of danger.)
Education can be countable when referring to the individual, specific educations of a set of people. Again, it’s more common, but not more correct, to use the uncountable version, as in “The youth of today dream of a high-quality education.” It carries a slightly different connotation though: that all are deprived of such, and collectively share that dream, while the countable construction focuses the reader slightly more on the individuality of the people mentioned.
Knowledge is much harder to use countably. The usual kind of construction for multiple knowledges is “fields of knowledge”, “knowledge domains”, and other similar constructions that place the plural on another noun. Wiktionary does include the countable version of knowledge and indicates that it can be used to mean multiple fields of knowledge. However, my experience is that plural knowledges is very rarely used, because it is rarely understood as clearly meaning “fields of knowledge”. When a word causes more confusion than clarity, it tends to lose currency.