Where does my.cnf get stored in Linux?
Most likely /etc/my.cnf or /etc/mysql/my.cnf.  Also check /home/username/my.cnf and /home/username/.mysql/my.cnf

If no luck there you can run

find / -type f -name my.cnf


That will scan you're entire disk where non priviledged access is allowed (which is fine; it should find it, i'm assuming your distro came with it and you're able to connect or you wouldn't be asking this much; but it will tie your disk up)