Another way I learned recently is to go to the terminal and type:
ps aux | grep postgres
which shows all the postgres processes running on your machine. From the list you should see one with the format ... -D .... E.G:
root 4155 0.0 0.0 2432908 68 ?? S 6May13 0:00.01 sudo su postgres -c /opt/local/lib/postgresql84/bin/postgres -D /opt/local/var/db/postgresql84/defaultdb -p 5432
the -D means directory. In the terminal, do a sudo su and then cd to that directory, and you’ll find the pg_hba.conf file.
And one more way:
Go to your terminal and type: locate pg_hba.conf. There should be a few results.