Look in src/config-files/krb5.conf in the MIT krb5 distribution.  If
you are using some other krb5 implementation, you'll need that
distribution's config file example - AFAIK config files are a local
manner and not covered by RFC1510 et al.

Also, krb5 config is a entirely separate issue from coda, with its own
complexities.  I'd strongly recommend that you get krb5 working to the
point where you have a kdc, 2 other client machines, and have eklogin
or something set up on one and can not only kinit but rlogin -x to the
other one.  I have no particular reason to be suspicious of the coda
krb code, but it strikes me as unwise to try coda as the first
kerberos application.

If I misunderstood, and you've already done this, I don't understand
why you need a sample config file.  I believe coda is simply a service
that uses kerberos, and doesn't impact configuration.  (I had krb4
coda almost set up a while ago, and don't now, so I'm not 100% sure.
However, I've never seen a kerberos service that required changing
krb5.conf.)