There are two ways to duplicate any campaign
1) - By going to the campaigns listing screen, click on "More" > "Duplicate" as explained in the image below:
Duplicating a campaign will result in creating an identical campaign of the original one.
2) - By going to your 'Campaign View' Screen and clicking on 'Clone'
This option will create an identical copy of your campaign (including all campaign settings), but is can only be used for Split-testing against the original campaign