1) Check if the Kobo shows as mounted drive in file manager (Windows Explorer, Mac Finder).
If not, the issue comes before you get as far as ADE and you need to check out details from Kobo.
Kobo must be plugged in by USB; wireless does not work for this.
2) Some ereaders need addiitonal software before ADE will recognise them. Not sure if that is true of the Kobo; check its manual.
3) ADE2 fails to see some ereaders. Try v1.7.2
There are lots of bugs in ADE2.0 (and 2.0.1). Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172
Some people have found ADE trying to upgrade automatically.
It appears (not 100% sure) that if you install ADE2.0 as a new install (not as an upgrade) that your 1.7.2 will continue to run.
Probably best to say no if 2.0.x installation asks if you want to migrate your library.