«قُلْ هَلْ يَسْتَوِي الَّذِينَ يَعْلَمُونَ وَالَّذِينَ لَا يَعْلَمُونَ»
Say: Are those who know equal to those who do not know?
In Qur'an 39:9, neither «يَعْلَمُونَ» nor «لَا يَعْلَمُونَ» is followed by a stated object. The purpose is not to discuss knowledge of one particular subject but to distinguish people characterized by knowledge from those lacking it.
Supplying a particular object would redirect the statement toward knowledge of that specified thing. The original contrast concerns the people and their differing qualities.