Queries gaining by adding a new index How would i be able to find out which queries would gain by adding a new index.

Ex: Lets assume i add a new NCI on a table , how would i be able to find out which queries would benefit from adding this NCI( or any Index ) for that matter of fact?
I'd second Jonathan's comments. There are many resources (to show the DBAs)showing that automated "missing indexes" analysis is very limited and often misleading.

In addition to sp_blitzindex, if you get them to run the following query against each database (after a representative uptime), you can get an idea of which tables are the cause of possibly unnecessary IO due to high number of scans (considering the row counts) and lookups. And you can start to consider the indexes suggested just for those tables, and/or find the offending queries and consider indexing for them. 

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED 
SELECT  OBJECT_SCHEMA_NAME(p.object_id) AS [Schema]
    , OBJECT_NAME(p.object_id) AS [Table]
    , i.name AS [Index]
    , i.type_desc AS [Index Type]
    --, p.partition_number
    , p.rows AS [Row Count],
       USER_SEEKS, 
       USER_SCANS, 
       USER_LOOKUPS, 
       USER_UPDATES
FROM sys.partitions p 
INNER JOIN sys.indexes i ON p.object_id = i.object_id
                         AND p.index_id = i.index_id
left join (select * from SYS.DM_DB_INDEX_USAGE_STATS  where DATABASE_ID = DB_ID(DB_NAME())) b ON b.object_id = i.object_id and b.index_id = i.index_id 
WHERE OBJECT_SCHEMA_NAME(p.object_id) != 'sys'