Joe, I found a machine on which I can reproduce the problem. I installed
wireguard-dkms-0.0.20190123-2.fc29.noarch
on top of
wireguard-dkms-0.0.20190123-1.fc29.noarch
but the machine while running
# dkms autoinstall
still returns
Error! Could not locate dkms.conf file.
File: /var/lib/dkms/wireguard/0.0.20181218/source/dkms.conf does not exist.
Actually I am leaving this place, so I will have no longer access to
this machine for a certain amount of time