After it is done, if you want to work with that library in PowerPhotos, add it to your library list. You can then use the Finder to copy the library to the location you want the copy to be. PowerPhotos will copy the library and, when it’s done, it will automatically appear in your library list. You will be prompted to choose a location to store the new copy of the library.
If you want to make an exact copy of one of your libraries, either as a backup or as part of moving a library to another disk, you can do so one of two ways.