فَإِنَّهُ مُحَالٌ ظَاهِرٌ، بِمَنْزِلَةِ قَوْلِنَا: أَسْوَدُ لَا سَوَادَ لَهُ
This is plainly incoherent, like calling something black while denying that it has blackness.
If 'black' is used genuinely and all blackness is then denied, the predicate is emptied of its content. The analogous objection asks how 'knowing' can be affirmed without any real knowledge.
Limit of the analogy: Blackness in a created object may be a contingent accident. Eternal divine knowledge is not therefore an accident, bodily color, or quality housed in an external subject. The example illustrates predication, not an identity of modes of existence.