Apex domains cannot have CNAME records.
Question and response
Question
dig pocosnet.nl. NS
Answer
pocosnet.nl. 5 NS ns2.sipo.nl.
pocosnet.nl. 5 NS ns1.sipo.nl.
pocosnet.nl. 5 NS ns3.sipo.nl.
Authority
The response has no authority records.
Additional
ns1.sipo.nl. 5 A 109.235.32.91
ns2.sipo.nl. 5 A 109.235.32.76
ns3.sipo.nl. 5 A 185.61.68.67
ns1.sipo.nl. 5 AAAA 2a03:be00:5:a:0:53:32:91
ns2.sipo.nl. 5 AAAA 2a03:be00:5:a:0:53:32:76
ns3.sipo.nl. 5 AAAA 2a03:be00:6:a:0:53:68:67
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0