There are two ways to duplicate any campaign:

1) - By going to the campaigns listing screen, and clicking on the "Duplicate" icon as shown in the image below:

Duplicating a campaign in this way will create a new and separate duplicate of this campaign (including any campaign variations it contained).

OR

2) - By going to your 'Campaign View' Screen and clicking on the 'Clone' icon:

This option will create an identical copy of your campaign as a new variation (inheriting all campaign settings), but is can only be used for Split-testing against the original campaign variation. The new campaign variation is created within the current campaign and will appear within the campaigns variation table.

How to Duplicate and split test my campaign