You can enable a general query log for that sort of diagnostic. Generally you don't log all SELECT queries on a production server though, it's a performance killer.
Edit your MySQL config, e.g. /etc/mysql/my.cnf
- look for, or add, a line like this:
log = /var/log/mysql/mysql.log
Restart mysql to pick up that change, now you can:
tail -f /var/log/mysql/mysql.log
Hey presto, you can watch the queries as they come in.