Apex domains cannot have CNAME records.
Question and response
Question
dig knockbot.jp. NS
Answer
knockbot.jp. 5 NS 04.dnsv.jp.
knockbot.jp. 5 NS 02.dnsv.jp.
knockbot.jp. 5 NS 01.dnsv.jp.
knockbot.jp. 5 NS 03.dnsv.jp.
Authority
The response has no authority records.
Additional
01.dnsv.jp. 5 A 157.7.32.53
02.dnsv.jp. 5 A 157.7.33.53
03.dnsv.jp. 5 A 157.7.34.53
04.dnsv.jp. 5 A 157.7.35.53
01.dnsv.jp. 5 AAAA 2400:8500:3300:0:0:0:0:53
03.dnsv.jp. 5 AAAA 2400:8500:3000:0:0:0:0:53
04.dnsv.jp. 5 AAAA 2400:8500:3fff:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0