Apex domains cannot have CNAME records.
Question and response
Question
dig udnemy.com. NS
Answer
udnemy.com. 5 NS ns3.udnemy.com.
udnemy.com. 5 NS ns2.udnemy.com.
Authority
The response has no authority records.
Additional
ns2.udnemy.com. 5 A 81.28.99.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0