Apex domains cannot have CNAME records.
Question and response
Question
dig gnudb.org. NS
Answer
gnudb.org. 5 NS ns3.datahjaelp.net.
gnudb.org. 5 NS ns1.datahjaelp.net.
gnudb.org. 5 NS ns2.datahjaelp.net.
Authority
The response has no authority records.
Additional
ns1.datahjaelp.net. 5 A 65.108.218.212
ns2.datahjaelp.net. 5 A 78.47.118.0
ns3.datahjaelp.net. 5 A 65.21.104.243
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0