Apex domains cannot have CNAME records.
Question and response
Question
dig grdns.it. NS
Answer
grdns.it. 5 NS ns.grdns.it.
grdns.it. 5 NS ns.grdns.cz.
Authority
The response has no authority records.
Additional
ns.grdns.cz. 5 A 81.2.194.104
ns.grdns.it. 5 A 95.110.254.167
ns.grdns.cz. 5 AAAA 2001:15e8:101:1:0:0:0:c268
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0