How to find out how much i/o resources a task, session, request or transaction is currently using?
If you are looking for the actual physical I/O for a query, you should look in the XML showplan for the 'ActualPhysicalReads' element:

schemas.microsoft.com/sqlserver/2004/07/showplan

However, those physical reads are likely only going to occur the first time the plan is cached. Subsequent runs are more likely to pull the pages from memory, not from disk. 

HTH