Apex domains cannot have CNAME records.
Question and response
Question
dig io.mk. NS
Answer
io.mk. 5 NS pns10.cloudns.net.
io.mk. 5 NS ns1.cloudns.net.
io.mk. 5 NS pns8.cloudns.net.
io.mk. 5 NS pns4.cloudns.net.
io.mk. 5 NS pns6.cloudns.net.
io.mk. 5 NS ns3.cloudns.net.
io.mk. 5 NS pns2.cloudns.net.
io.mk. 5 NS ns2.cloudns.net.
io.mk. 5 NS pns3.cloudns.net.
io.mk. 5 NS pns1.cloudns.net.
io.mk. 5 NS pns5.cloudns.net.
io.mk. 5 NS pns7.cloudns.net.
io.mk. 5 NS ns4.cloudns.net.
io.mk. 5 NS pns9.cloudns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0