Apex domains cannot have CNAME records.
Question and response
Question
dig core.kcom.com. NS
Answer
core.kcom.com. 5 NS bison.kcom.com.
core.kcom.com. 5 NS ibex.kcom.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0