question

This is a very vague question that could get a really complicated solution. If you simply want to locate a duplicate row then you will need to use something like:

USE [adventureworks]
GO
CREATE TABLE Myduplicates
    (
      IDCol INT IDENTITY,
      ColA varchar(20),
      ColB VARCHAR(10),
      ColC int
    )
GO
INSERT  INTO [dbo].[Myduplicates] ( [ColA], [ColB], [ColC] )
        SELECT  'Larry', -- ColA - varchar(20)
                'Curly', -- ColB - varchar(10)
                10  -- ColC - int
        UNION
        SELECT  'Larry', -- ColA - varchar(20)
                'Moe', -- ColB - varchar(10)
                20  -- ColC - int
        UNION
        SELECT  'Curly', -- ColA - varchar(20)
                'Larry', -- ColB - varchar(10)
                30  -- ColC - int
        UNION
        SELECT  'Moe', -- ColA - varchar(20)
                'Curly', -- ColB - varchar(10)
                10  -- ColC - int
        UNION
        SELECT  'Zeppo', -- ColA - varchar(20)
                'Harpo', -- ColB - varchar(10)
                10  -- ColC - int
        UNION
        SELECT  'Chico', -- ColA - varchar(20)
                'Zeppo', -- ColB - varchar(10)
                30  -- ColC - int
        UNION
        SELECT  'Groucho', -- ColA - varchar(20)
                'Zeppo', -- ColB - varchar(10)
                20
  -- ColC - int
go

SELECT  [m].[ColA],
        COUNT(idcol) AS [duplicate count]
FROM    [dbo].[Myduplicates] AS m
GROUP BY [m].[ColA]
having  COUNT(idcol) > 1
ORDER BY [duplicate count] DESC ;

SELECT  [m].[Colb],
        COUNT(idcol) AS [duplicate count]
FROM    [dbo].[Myduplicates] AS m
GROUP BY [m].[Colb]
having  COUNT(idcol) > 1
ORDER BY [duplicate count] DESC ;

SELECT  [m].[Colc],
        COUNT(idcol) AS [duplicate count]
FROM    [dbo].[Myduplicates] AS m
GROUP BY [m].[Colc]
having  COUNT(idcol) > 1
ORDER BY [duplicate count] DESC ;

SELECT  [m].[IDCol] AS [IDs that need review for ColA duplicates]
FROM    [dbo].[Myduplicates] AS m
        INNER JOIN ( SELECT [m].[ColA],
                            COUNT(idcol) AS [duplicate count]
                     FROM   [dbo].[Myduplicates] AS m
                     GROUP BY [m].[ColA]
                     having COUNT(idcol) > 1
                   ) AS s1 ON [m].[ColA] = [s1].[ColA];

SELECT  [m].[IDCol] AS [IDs that need review for ColB duplicates]
FROM    [dbo].[Myduplicates] AS m
        INNER JOIN ( SELECT [m].[Colb],
                            COUNT(idcol) AS [duplicate count]
                     FROM   [dbo].[Myduplicates] AS m
                     GROUP BY [m].[Colb]
                     having COUNT(idcol) > 1
                   ) AS s1 ON [m].[Colb] = [s1].[Colb];

go
DROP TABLE Myduplicates

resolving the duplicates will be a whole new piece of work

There are a number of ways to solve this using TSQL. The best these days seem to revolve around using ROW_NUMBER(). The key is to simply understand the basic concept that you need a method to uniquely identify the row. Then you need a way to mark duplicate values for that unique identifier and then you need a mechanism to remove those duplicates. While this sounds like three steps, you should be able to do all this in a single query.

I hope that I understand the question correctly. The task is to find the duplicate records across all columns in the table. I will also provide the sample of how to quickly delete all such duplicates. Lets create a heap table and insert some records in it (including some duplicates:

create table #t (a int, b int);
go

insert into #t values (1, 1);
insert into #t values (1, 1);
insert into #t values (1, 1);
insert into #t values (1, 1);
insert into #t values (2, 5);
insert into #t values (2, 5);
insert into #t values (3, 1);
insert into #t values (4, 6);
insert into #t values (4, 6);
go

Now we have 4 occurences of (1, 1); 2 occurences of (2, 5); (3, 1) does not have any duplicates and we also have 2 occurences of (4, 6). Here is the script to quickly identify all the duplicates:

select
        row_number() over (partition by a order by a) PartitionedNumber, *
        from #t;

Here is the result of the query above:

PartitionedNumber    a           b
-------------------- ----------- -----------
1                    1           1
2                    1           1
3                    1           1
4                    1           1
1                    2           5
2                    2           5
1                    3           1
1                    4           6
2                    4           6

Suppose we want to get rid of all dups while preserving all unique rows. In other words, the end result is expected to have #t with one (1, 1) record, one (2, 5) record, one (3, 1) record, and one (4, 6) record,. The statement to do this can be like this:

with records (PartitionedNumber, a, b) as
(
        select
                row_number() over (partition by a order by a) PartitionedNumber, *
                from #t
)
        delete records where PartitionedNumber > 1;

The above will delete all dups preserving the unique records only.