Apex domains cannot have CNAME records.
Question and response
Question
dig forma.sk. NS
Answer
forma.sk. 5 NS ns2.forma.sk.
forma.sk. 5 NS ns1.forma.sk.
forma.sk. 5 NS ns.forma.sk.
Authority
The response has no authority records.
Additional
ns.forma.sk. 5 A 194.160.65.99
ns1.forma.sk. 5 A 194.160.65.98
ns2.forma.sk. 5 A 135.181.56.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0