Where does the Android Version of OneNote store it's data?

OneNote for Android does not have the ability to save the notes locally. All your notebooks are stored on SkyDrive.
Log-in with your SkyDrive account to access the notebook from another PC and then save/backup the notebooks from there.

Please fact check your replies prior to replying, as this is factually incorrect.  OneNote saves all data locally so it's available offline, otherwise it defeats the purpose of OneNote.  OneDrive is different, as it's purpose is server [cloud] based storage.

As to where OneNote Android saves the data, it's located within directory:

•  ./data/data/com.microsoft.office.onenote/Microsoft/Office Mobile/SPM Data/File Store/1000/https/d.docs.live.net/<account specific hexadecimal folder>

and requires root access to get to.  The data is saved by GUID and even if you were to copy the correct section and rename it with the correct GUID, OneNote Android wouldn't recognize the data, as there's numerous database files that tells OneNote android the data is there.  These database files aren't easily editable for security reasons 

OK how do we change the card or the folder where the data is stored

My notebooks are large and they are continuously growing due to my intense work mostly done on my desktop

From there the changes are pushed to my android phone and tablet but we seem to have no control over how large these files become and no way to easily monitor their size and relocate these files to another drive if need it

What do you mean by card or folder where the data is stored?

• If you're referring to a microSD card in a phone, it's not possible to store notebooks there.  To understand why, please read my prior post, as well as see my posts on page 2 of OneNote for Android stuck at 'setting up OneNote'?
• If you're referring to a different data folder on an Android device, the above bullet would apply here as well.

The problem is not the overall size of the notebook persay, but how large it is during the initial sync from OneDrive to the Android device.  Once the initial sync occurs and everything is fully synced over, as long as you sync the Android OneNote app whenever you add in excess of ~10MB to a notebook, no other issues will should appear. 

• 10MB is an arbitrary number and is, at most, the easiest and most convenient way to ensure an end user does not experience issues after the initial sync.  The size amount that would cause a sync issue is likely much higher, however, since there's no way to know what that size amount would be without doing some serious debugging into the OneNote app, I'd recommend sticking in the ~10MB area.
• Keep in mind 10MB of notebook content is quite a lot if one one isn't attaching files directly to notes.

When changes are made on a PC, they aren't pushed from the PC to the device - they're synced to OneDrive, then once the OneNote app is opened (or synced if already opened), it downloads the changes from OneDrive.  If you're constantly syncing large notebook changes after the initial sync, there isn't an easy solution.  You should be able to monitor how large a change to your notebook has been via the OneNote PC program, and/or comparing the size of your notebook on OneDrive prior to, then after, a change.

• If you're requiring immediate access on a device once a change has been made via a PC, a surefire workaround would be to create a temporary notebook and name it Temp.  You can then copy [not move, just copy] the tab(s) that was/were changed to the Temp notebook, which will ensure the content is available on the Android device without issue

In regards to the initial sync (such as on a new device, or a device that's been factory reset, and/or had it's data partition formatted), the best way to avoid the headache is to have a backup app (there's numerous variations; I use MyBackup Pro by Rerware) backup the app data for the OneNote app.  Then on the new device, you'll need to first setup the OneNote app by logging in, then force close the app via the Android Settings - App menu.  Once this has occurred, you can then restore the app data that was backed up previously.  

• You may also want to try doing a maintenance task on your Notebooks.
  1. Optimize your notebooks: Options -> Save & Backup -> Optimize All Files Now
•  Additionally, this info may or may not help you

I highly recommend all users experiencing this issue to make their complaints known to Microsoft.  OneNote is a phenomenal piece of software, however the way in which their Android team coded the Android app is problematic, and combined with the fact their Android team has been made aware of this for over two years and still not fixed the issue speaks to a level of incompetency within the Android team that coded this app

On occassion I might send to OneNote web pages with large images included by the webmaster or chose myself to attach large files

In this case the notebooks might end up using a lot of space on the Android device which is not something that we can control. The location of these files (I well understood your initial point) is in a folder that we can not see withiout rooting the device.

My q is what happens when you reach the limit of your storage capacity on that card where the hidden folders reside. Can you config onenote to move its stuff on the second SD card that you might have attached ?

So, my q was not about how the sync is done and so on

You can move app data storage to an external microSD card, however you have to be rooted and configure the device with an app like apps2sd.  However I don't believe this is possible on Android 5+ due to SELinux. You'll want to do some research via Google for your device, as well as check out your device's forum page on XDA Developers.

As to what happens if you fill up the system partition with app data, your device will function poorly.  You'll get numerous notifications from the system that you're running out of, or have run out of free space.  You can view how much your notebooks, as a whole, are taking up on the device via the app details screen for OneNote under Settings - Apps.

• The caveat however is temporary file fragments will build up from failed syncs in the folder path a few posts back, and rebooting the device doesn't always  remove those file fragments.  For example, I had GB of file fragments, which increased the amount of storage OneNote data took up to more than twice the size of the notebooks.

If you are running out of storage due to the OneNote data, the only other alternative would be to create a specific notebook for Android and only sync that specific notebook with only the specific content needed for accessibility from Android.

• Another work around would be to view the content in a browser instead of the OneNote app.  This would take the app and app storage completely out of the equation.  Go to https://www.onenote.com/notebooks

OK so there is no easy way

Thanks for the above details,

My decision (already taken before posting here) was to have just my reading queue in OneNote drive and sync just this with the Desktop. When I am done with the article I release the space by moving the article from the cloud to the desktop only notebook

I was looking for a less attention consuming method. 

I am still on 4.1 so maybe rooting the device and try what you suggested will do it down the road