A few small suggestions:
ἐπαινέω is a better word for 'praise.' This is what is used in Plato's dialogues in a similar context (to name one example).
Abstract nouns often take the article; hence, τὴν ἀγνωσίαν. Likewise nouns referring to an entire class: ὁ ἄνθρωπος, 'man,' i.e. the human race.
I have a sense that the word order of the last part could be polished up a little bit. Putting it all together, I would say:
ἐπαίνει τὴν ἀγνωσίαν· ὃ γὰρ οὐχ εὕρηκεν ὁ ἄνθρωπος οὐκ ἀπολώλεκεν.
Or, if you don't want it to be a command to a single individual, but a general statement, "One should praise..." you could use one of the verbal adjective in -τέον (Smyth 2149-52):
ἐπαινητέον τὴν ἀγνωσίαν....
Dic mihi, Damoeta, 'cuium pecus' anne Latinum?