Just go to your on board storage or Micro SD card. Then just make a folder called Notifications. Then put your files into this folder. Done, nothing else needed. You don't need to place that Notifications folder in any particular location. I have mine sittinng in: /mnt/sdcard/notifications and for ringtones if have them in /mnt/sdcard/ringtones.
Now if you have an Micro SD card and rather save space on your on board storage, then you can just put the files in /mnt/extSdCard/notifications for notifications and /mnt/extSdCard/Ringtones for ringtones.
BTW, if your uploading the files to your dropbox from your pc, why not just quickly connect your device to your pc and drag and drop the files to your Note 2 at the same time.