need more data.
unfortunately, the content of honey is not pure so the resistance per mm will not be constant.
the two nail probe used for soil moisture, or wood moisture is a possibility, but the base resistance would need to be known.
a humidity sensor used to detect the moisture in air could be used if you have a closed environment for your honey. say inside of the hive
do you need an instant (more or less) you would need to use a refractometer. I have not seen one for use with an arduino.