Apex domains cannot have CNAME records.
Question and response
Question
dig demax.sk. NS
Answer
demax.sk. 5 NS ns1.demax.sk.
Authority
The response has no authority records.
Additional
ns1.demax.sk. 5 A 195.62.16.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0