Apex domains cannot have CNAME records.
Question and response
Question
dig onexs.nl. NS
Answer
onexs.nl. 5 NS ns3.openprovider.eu.
onexs.nl. 5 NS ns2.openprovider.be.
onexs.nl. 5 NS ns1.openprovider.nl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0