Apex domains cannot have CNAME records.
Question and response
Question
dig gtld-servers.Net. NS
Answer
gtld-servers.NET. 2 NS av4.nstld.com.
gtld-servers.NET. 2 NS av3.nstld.com.
gtld-servers.NET. 2 NS av1.nstld.com.
gtld-servers.NET. 2 NS av2.nstld.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0