While deleting a row from a normal grid, how do I get the index of the deleted r

I just saw you mention normal grid.
try this:- add a hidden numeric column to your grid and populate the data via this code
enumerate(yourCDT.size)
Save the value into an ACP (say rowIndexer)
on the DATA-> output, do difference(enumerate(cdt.length), acp!rowIndexer)
This will give you the index of the row that was deleted. You can use remove() function to remove this from the CDT array either in the same place or in a different script task.

I just saw you mention normal grid.
try this:- add a hidden numeric column to your grid and populate the data via this code
enumerate(yourCDT.size)
Save the value into an ACP (say rowIndexer)
on the DATA-> output, do difference(enumerate(cdt.length), acp!rowIndexer)
This will give you the index of the row that was deleted. You can use remove() function to remove this from the CDT array either in the same place or in a different script task.