Apex domains cannot have CNAME records.
Question and response
Question
dig dynamic-ip.pni.hk. NS
Answer
dynamic-ip.pni.hk. 4 NS ns1.pni.tw.
dynamic-ip.pni.hk. 4 NS ns2.pni.tw.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0