Apex domains cannot have CNAME records.
Question and response
Question
dig koaladns.com. NS
Answer
koaladns.com. 4 NS ns-canada.topdns.com.
koaladns.com. 4 NS ns-usa.topdns.com.
koaladns.com. 4 NS ns-uk.topdns.com.
Authority
The response has no authority records.
Additional
ns-uk.topdns.com. 4 A 77.247.183.137
ns-usa.topdns.com. 4 A 143.198.68.197
ns-usa.topdns.com. 4 A 161.35.225.48
ns-canada.topdns.com. 4 A 109.201.142.225
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0