What is the query in the report? Can you post it here?
If the report is a static query, just create a text box and paste the query in there.
If the query is a stored proc then that won't work, and what Anthony suggested won't work either because the XML will just give you the stored proc command.
If the query has parameters, you can use an expression to build a string with the query
="select columns from table where field = '" + Parameters!Parameter1.value "'"
Why do you want to do this? Most users should not be looking at the query, just it's results. If you want to show what parameters have been selected, just add them to the report header or text boxes like "Parameters!Parameter1.value"
If it's for debugging purposes then why not just intercept the query in SQL Profiler.