I just received the following question:
I will like to know how I can see the duplicates in a selection data? I'm aware I can delete duplicates, however I will like to know how to identify them first before deleted.

Here's how to do this:

You can use the following tool to select the cells with duplicated values:
Select » Select cells based on content, formatting and more...

To count and/or color the cells that are duplicated, you can use the following tool:
Range » Count and/or color duplicates in selection...

For your information, the following utility only removes the duplicated entries, leaving one original for each value:
Range » Clear duplicated values in selection (leave one original)