adb pull file from /data/data
This is possible if the ADB daemon on the device runs with root privileges – which can be achieved e.g. using chainfire's adbd Insecure:


adbd Insecure (source: Google Play; click image to enlarge)

Another possibility would be setting ro.secure to 0 in the build.prop or default.prop. To my experience, adbd does not honor this on all devices/ROMs.