To copy a workflow you first need to open the workflow for edit.
Now you should click the arrow next to the save option on the upper right to display the save options:
Here you have two options for copying the workflow:
1.Save as Copy
With this option you are prompted e.g. for a name for the new workflow with this pop up window:
The suggested name is always the original name with 'Copy of ' added, and the group as well as description are prefilled with the same as the original workflow.
You need yourself to setup the input in order to prevent the copy of the workflow to conflict with the original workflow.
2.Download
If you select download of the workflow, then the workflow will as default be copied to your download folder as the name of your workflow with the extension, .json.