NOTE: If you delete the app and reinstall it, you will delete your sketches. Even if you are logged in....
----
All sketches are local to the device. You need to back it up manually:
For iOS, the best method is to use the iCloud:
https://www.sketchbook.com/help/knowledge-base/how-save-your-work/
https://www.sketchbook.com/help/knowledge-base/use-icloud/
IMPORTANT: To save a copy or version a file so you don't lose progress on the Mobile platform:
a. Start Sketch
b. Go to Gallery and start a new Sketch, It will ask you to save the file.
c. Go to the Gallery and start a new Sketch again and it will ask you to save the file.
d. Open the first Sketch and work on it.
e. Go to Gallery and start new sketch and choose the "Save as a Copy" option.
David Lau