Apex domains cannot have CNAME records.
Question and response
Question
dig o05.xemis.net. NS
Answer
o05.xemis.net. 5 NS f05.oxemis.net.
o05.xemis.net. 5 NS ns.o05.xemis.net.
o05.xemis.net. 5 NS nssec.online.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0