Apex domains cannot have CNAME records.
Question and response
Question
dig time.com.kh. NS
Answer
time.com.kh. 5 NS blue.foundationdns.net.
time.com.kh. 5 NS blue.foundationdns.org.
time.com.kh. 5 NS blue.foundationdns.com.
Authority
The response has no authority records.
Additional
blue.foundationdns.com. 5 A 108.162.198.1
blue.foundationdns.com. 5 A 162.159.60.1
blue.foundationdns.com. 5 A 172.64.40.1
blue.foundationdns.net. 5 A 108.162.198.31
blue.foundationdns.net. 5 A 162.159.60.31
blue.foundationdns.net. 5 A 172.64.40.31
blue.foundationdns.org. 5 A 108.162.198.61
blue.foundationdns.org. 5 A 162.159.60.61
blue.foundationdns.org. 5 A 172.64.40.61
blue.foundationdns.com. 5 AAAA 2606:4700:57:0:0:0:6ca2:c601
blue.foundationdns.com. 5 AAAA 2803:f800:52:0:0:0:a29f:3c01
blue.foundationdns.com. 5 AAAA 2a06:98c1:56:0:0:0:ac40:2801
blue.foundationdns.net. 5 AAAA 2606:4700:57:0:0:0:6ca2:c61f
blue.foundationdns.net. 5 AAAA 2803:f800:52:0:0:0:a29f:3c1f
blue.foundationdns.net. 5 AAAA 2a06:98c1:56:0:0:0:ac40:281f
blue.foundationdns.org. 5 AAAA 2606:4700:57:0:0:0:6ca2:c63d
blue.foundationdns.org. 5 AAAA 2803:f800:52:0:0:0:a29f:3c3d
blue.foundationdns.org. 5 AAAA 2a06:98c1:56:0:0:0:ac40:283d
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0