Husires and dkbit are right, you need root privileges to be able to see and access the wallet file. You will have to root your device to be able to copy the wallet file and transfer it to another device. I don't recommend doing this for security reasons.
Why is this even necessary? All Electrum would need, theoretically, is the user permission to access the user's files in order to make its own directory to store the backups, and restore from them as well. Root access should not be required to access the backup file.