In case somebody has this similar problem:
I used the following two commands to replace the non-UTF-8 copyright symbol in several hundred course.conf files that we had to move to a new server using the latest ww_version 2.15:
sudo sed -i "s/\xa9/'\©'/g" /opt/webwork/courses/*/course.conf
sudo sed -i "s/\xef\xbf\xbd/'\©'/g" /opt/webwork/courses/*/course.conf