You can use any one of these filters from /wp-includes/query.php
posts_where_request
posts_groupby_request
posts_join_request
posts_orderby_request
posts_distinct_request
posts_fields_request
post_limits_request
You can print certain parts of the query to the screen to see what’s going on under the hood.
For instance, you can add this to your functions file:
add_filter('posts_where_request', 'foo_bar', 1, 10);
function foo_bar($where){
print_r($where);
return $where;
}