As the name implies, this node lets you pick one or many columns and creates a copy of each.
Add Duplicate Column to any node in your Dataflow. Select any node and use the Transform (+) button to open the list of options to select d Duplicate Column. You could work with the node in the Dataflow tab or use the Properties panel.
The Duplicate Column node is broken up into:
Using the dropdown, select the first column you would like to duplicate.
Use the text box to enter a new name for the resulting column.
Click the +Duplicate Another button and pick the second column - you could add more than two.
To change the order of new columns, click and hold the drag handle on the left of a column. Then drag the column up or down. New columns are added from left to right, and the order will match the top to bottom order in the node.