Apex domains cannot have CNAME records.
Question and response
Question
dig sisc.com. NS
Answer
sisc.com. 5 NS kirk.ns.cloudflare.com.
sisc.com. 5 NS rachel.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0