Apex domains cannot have CNAME records.
Question and response
Question
dig omnisdns.net. NS
Answer
omnisdns.net. 5 NS ns1.omnis.com.
omnisdns.net. 5 NS ns2.omnisdns.net.
Authority
The response has no authority records.
Additional
ns1.omnis.com. 5 A 216.239.128.2
ns2.omnisdns.net. 5 A 204.10.136.2
ns1.omnis.com. 5 AAAA 2607:fe90:8000:0:0:0:0:2
ns2.omnisdns.net. 5 AAAA 2607:fe90:8001:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0