To get the query memory usage of currently executing queries run the following:
SELECT
TEXT
,query_plan
,requested_memory_kb
,granted_memory_kb
,used_memory_kb
FROM sys.dm_exec_query_memory_grants emg
CROSS APPLY sys.dm_exec_sql_text(sql_handle)
CROSS APPLY sys.dm_exec_query_plan(emg.plan_handle)
ORDER BY emg.requested_memory_kb DESC