The affix ka comes after the root dā 'to give' and jña 'to know', when taking the preposition pra in composition with a word in the Accusative -2nd case.,
We applied by sutra 3 the affix क after verbs that ended in long आ and had no upasarga. Now begins the case of verbs with upasarga. This debars the affix अण्; as सर्वप्रदः 6.4.64 'giver of all; liberal', पथिप्रज्ञः 6.4.64 'acquainted with roads'. The long आ of दा and ज्ञा is elided by 6.4.64.
Why do we say 'when taking प्र'? With any other upasarga these verbs will take the general affix अण्; as गोसन्दाय.,