Apex domains cannot have CNAME records.
Question and response
Question
dig mobi. NS
Answer
mobi. 5 NS b0.mobi.afilias-nst.org.
mobi. 5 NS a0.mobi.afilias-nst.info.
mobi. 5 NS a2.mobi.afilias-nst.info.
mobi. 5 NS d0.mobi.afilias-nst.org.
mobi. 5 NS c0.mobi.afilias-nst.info.
mobi. 5 NS b2.mobi.afilias-nst.org.
Authority
The response has no authority records.
Additional
a0.mobi.afilias-nst.info. 5 A 199.254.55.1
b0.mobi.afilias-nst.org. 5 A 199.254.56.1
c0.mobi.afilias-nst.info. 5 A 199.254.57.1
d0.mobi.afilias-nst.org. 5 A 199.254.58.1
a0.mobi.afilias-nst.info. 5 AAAA 2001:500:21:0:0:0:0:1
b0.mobi.afilias-nst.org. 5 AAAA 2001:500:22:0:0:0:0:1
c0.mobi.afilias-nst.info. 5 AAAA 2001:500:23:0:0:0:0:1
d0.mobi.afilias-nst.org. 5 AAAA 2001:500:24:0:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0