Hi Shreyas,
Hope you are doing well. If you have got a proof that your mother tongue is Kannada in actual, you may fall under the category of SCK. Otherwise SC candidates who don't have any proofs regarding their mother tongue may fall under the category SCG. The accepted proofs during K-CET document verification for mother tongue will include the Transfer Certificate or Domicile Certificate or any other valid certificate in which the mother tongue is clearly mentioned. I hope you got the point after reading this answer.

All the best.