Apex domains cannot have CNAME records.
Question and response
Question
dig cs.wisc.edu. NS
Answer
cs.wisc.edu. 5 NS adns4.doit.wisc.edu.
cs.wisc.edu. 5 NS adns2.doit.wisc.edu.
cs.wisc.edu. 5 NS adns1.doit.wisc.edu.
cs.wisc.edu. 5 NS adns3.doit.wisc.edu.
Authority
The response has no authority records.
Additional
adns1.doit.wisc.edu. 5 A 144.92.9.21
adns2.doit.wisc.edu. 5 A 144.92.20.99
adns3.doit.wisc.edu. 5 A 144.92.104.21
adns4.doit.wisc.edu. 5 A 128.6.1.132
adns1.doit.wisc.edu. 5 AAAA 2607:f388:0:0:0:0:a53:1
adns2.doit.wisc.edu. 5 AAAA 2607:f388:0:0:0:0:a53:2
adns3.doit.wisc.edu. 5 AAAA 2607:f388:0:0:0:0:a53:3
adns4.doit.wisc.edu. 5 AAAA 2620:0:d60:6:0:0:0:12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0