log sql query execution

Question

SQL Server 2008 - I have a BigQuery contain select query with multiple sub queries,temp table, lot of if conditions.
How to see which select query sub query is return null or value and see temp table's data, terminate or not if conditions such
things? Is it possible to create LOG table to see the query execution ? If creating LOG table is such a good way, then how to use
LOG table in the Bigquery? Kindly advise me, please.