The origin is the proto-germanic word kunnan, which means “to recognise, to know (how to be able)”.
According to Wikipedia, the first known usage of the phrase by the German poet Johann Gottfried Herder is actually a bit more complex and references both the knowing and the being able to:
“Kunst kommt von Können oder Kennen her (nosse aut posse), vielleicht von beiden, wenigstens muß sie beides in gehörigem Grad verbinden. Wer kennt, ohne zu können, ist ein Theorist, dem man in Sachen des Könnens kaum trauet; wer kann ohne zu kennen, ist ein bloßer Praktiker oder Handwerker; der echte Künstler verbindet beides.”
Quick and dirty translation:
“Art is derived from being able to do and knowing, maybe from both, at least art must combine both in proper measure. Who knows, without being able, is a theorist, whom one cannot trust with regards to being able to do; Who can without knowing, is a mere practician or craftsman; the real artist connects both.”
By the way, I don’t know you, I don’t want to offend you and the very little info I have from your comment is evidence that you’re a intelligent, well educated, open-minded and complex person…. but to be honest, when I see the phrase “Kunst kommt von Können” my first association is of a narrow-minded square, who doesn’t like anything they are not familiar with. Again, this is not directed at you, I just wanted to share what kind of associations this phrase creates in me in general from my personal, limited experience with people, who used it.