Apex domains cannot have CNAME records.
Question and response
Question
dig klinux.it. NS
Answer
klinux.it. 1 NS ns3.klinux.it.
klinux.it. 1 NS ns0.klinux.it.
klinux.it. 1 NS ns1.klinux.it.
klinux.it. 1 NS ns2.klinux.it.
Authority
The response has no authority records.
Additional
ns0.klinux.it. 1 A 151.236.56.210
ns1.klinux.it. 1 A 135.125.219.232
ns2.klinux.it. 1 A 217.182.86.138
ns3.klinux.it. 1 A 54.39.177.90
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0