kathaṃ nāstyasya vedanam iti / tasyāpi nīlādisvabhāvavad upalabdhilakṣaṇaprāptatvādyuktam eva saṃvedanam ityabhiprāyaḥ
"Why is there no cognition of it?" means that since it [sound] also fulfills the conditions of perceptibility like blue and other [things], its cognition should certainly occur