Enable Slow Query Logging in mysql 5.6

This tutorial will show you the settings you need to make in order to enable slow query logging

slow_query_log = 1  <0|1>
log-queries-not-using-indexes <if you want to log all queries that don't use indexes>
long_query_time=1   <Set this to the number of seconds a query must take to be considered "slow">
log-slow-queries=/var/log/mysql/log-slow-queries.log <Log file path>