we would understand it in this direction
group the data on colA, colB
From the group members take the last member (as we do see NOK and not OK)
5699510 information OK
5699510 information NOK
dt2 =
(From d in dt1.AsEnumerable
Group d by k1 = d("ColA").toString.Trim,k2 = d("ColB").toString.Trim into grp=Group
Select r = grp.Last()).CopyToDaTable
Modify ColA, ColB name or index to your details
Also have a look here: