When you import a file of data you are able to easily view all the fields and values in those fields by simply browsing the data in the spreadsheet. However if you connect to a data source directly it is much hard to view everything that comes out of it. There is a way of doing this though.

Instead of importing the data into RE, you can set up each action to take as "Ignore". That way all the data will go into the control report. You are then able to look at the file of "exceptions" i.e. all the rows that you chose to ignore inside the control report instead.

As a further tip, if you have very many rows, instead of manually updating each one to ignore, select the filter button on the review screen: 

You can then select all rows that are currently "Create" and change them to "Ignore". You can repeat this for any rows that are "Update" or "Decide" too.