Hi,
TL;DR;? --> jump to the numbered questions directly. 
I recently tried to help a women who contacted us (Hamburg heaven) because her phone seem to be broken (charging issues, than it seemed that it will be uncharged while the charger was connected, than it was not able to turn it at all). She already had a lot of contact to the support as well as to a local Telekom shop. She was sad as she had about 2 year of photos on it. The Telekom shop just helped her to save some data from the external sd-card, but there were only some photos on it. As all the contact with the local shop and the German support took quite long she gave up. She is also not that familiar to this technical stuff (even she already opened her phone on her own and cleaned the part-connectors and so on).
Anyway. I met her last week and the technical problems were resolved quickly. I put in a used but still working battery and we changed the bottom module as the charger or usb-cable connection to the PC/laptop was a a bit unstable. So the phone is basically working again. She also told me that she accidentally accessed the recovery menu (an older TWRP is on it) and she assured that she just rebooted as she did not know what it is or how to use it (at this time it still was possible to turn the phone on). She saw the welcome screen + setup assistant. So the phone looked like reset. She assured that she has not performed a factory reset (or at least not knowingly). So now we were at the same state when we met: welcome screen + setup assistant
So enough of the history. The phone is working. The questions I have:
- Is there a way how I can see if a factory reset took place?
The second question probably depends on if a factory reset was performed (and if it really [completely] overwrites the internal storage).
Or in other words - if there is a chance that there is still data on the internal sd-card - we can discuss question 2.
- How to rescue data from the internal storage of a phone?
In an XMPP MUC I got the following tip.
Connect the phone via adb (should work via TWRP) -> create an image via dd -> scan the image with an application like testdisk or photorec (I know neither of them yet, but I would give it a try).
Thanks for any help. I never used these kind of recovery tools on a phone (backup up the data frequently is less stressful ). I just remember that there was a chance to get some data back on partially broken spinning disks (e.g. filetable or bootsector broken). I don’t have any idea if there is a chance on flash disks / sd-cards at all.
PS.:
I’m familiar with adb, twrp, flashing recovery or an alternative OS etc. So you don’t have to start at point zero . Nevertheless if anybody already tried some data recovery, feel free to share including commands etc. … I use a Debian based Linux OS so it would speed the whole thing up if we do not depend on any Windows or MacOS only tools.