from here

Copy it from internal to SD card, then ADB pull from SD card to host machine.

$ adb shell
# if you have multiple devices, adb -s  shell
$ run-as {app-package-name}
$ cd /data/data/{app-package-name}
$ chmod 777 {file}
$ cp {file} /mnt/sdcard/
$ adb pull /mnt/sdcard/{file}