I had the same question. I wanted to know the version to decide whether to reference a particular class which didn't exist in versions earlier than SDK 23.
Then I realised there was a better way.
try:
AudioFocusRequest = autoclass('android.media.AudioFocusRequest')
except jnius.JavaException:
# Not available on earlier versions of Android.
AudioFocusRequest = None
Now, I don't need to know what the version actually is, and there won't be any bugs where I get the threshold values wrong. I just check whether the AutoFocusRequest exists before I use it.