The affix ḍatamac (atama with the elision of the last syllable) comes after kim , yat and tat , optionally when the object is the determining of the one out of many, the question being that of caste. ,
The words किंयत्तदः and निरर्धारणे एकस्य are to be read into the sutra. Thus कतमो भवतां कठः 'which of you, Sirs, is a Katha Brahmana?' यतमो भवतां कठः, ततम आगच्छतु 'that one of you, Sirs, who is a Katha, let him come'. The word वा 'optionally' indicates that the affix अकच् 5.3.71 also comes, as यको भवतां कठः, तकः, आगच्छतु ॥ This idea may be expressed by a sentence also, owing to the महाविभाषा 4.1.82: as, को भवतां कठः; यो भवतां कठः, स आगच्छतु ॥
Why do we say 'when question is that of caste'? Observe, को भवतां देवदत्तः. Here the question is about a Name: and not jati. The word परिप्रश्न applies to किम् only, the pronouns यत् and तत् not being interrogative pronouns. But the word जाति applies to all these three pronouns.
According to some, the affix डतर has also this force, after the word किम्, as, कतरो भवतां कठः 'which of you, Sirs, is a Katha Brahmana?' कतरो भवतां कलापः. As may be inferred from the sutra कतरकतमौ जातिपरिप्रश्ने 4.1.63,