If you want to find the location of your log file in Postgres, you'll need to hop into a Psql session..
Then it's as simple as running..
show data_directory ;
Which will output the data directory, in my case..
To see the file name run..
show log_filename ;
There are other useful commands too. You can read more of them here https://www.postgresql.org/docs/9.3/static/runtime-config-logging.html