Specifically:
The archive of newgroup and rmgroup messages is in a directory per
top-level hierarchy and the archive is gzipped. It's in Berkeley Mail
format, intended to be read with a mail client, but you can read it with
any text display program.
ftp://ftp.isc.org/pub/usenet/control/news/news.groups.gz
With a genuine FTP client from the command line as gawd intended:
pftp
ftp.isc.org
cd pub/usenet/control/news
get news.groups.gz
exit
gunzip -N news.groups.gz
and then you'll be able to read it.
The newgroup message is the proponent's concept of what's on topic in
the group. In practice, its users decide what to discuss, so don't use
the newgroup message to flog anyone you deem to be off topic 'cuz
that's, you know, obnoxious.
Russ's README
ftp://ftp.isc.org/pub/usenet/control/README
explains the syntax of a newgroup or rmgroup message so it gets
archived, together with what hierarchies are recognized (in
control.ctl).
But lack of a Newsgroups file line will prevent the News server at ISC
from adding an entry to the sample active and newsgroups files.
ftp://ftp.isc.org/pub/usenet/CONFIG/README
the other Russ's README