How is the best way to water a rubber plant? How much , how often; from above or below?

Water you rubber tree thoroughly when the soil has had a chance to dry, but not dry for so long, time the leaves fall off. It depends on the soil when you would need to water. Watering is never a set schedule.
You might need to water every week or every couple of weeks. Do the finger test to make sure the soil is not still wet before watering. If you have trouble reaching way down to check the soil, you might be able to feel the soil through the drainage hole.Rubber trees hate constant wet feet.
I guess how you water is everyones own preference. I prefer to water all my plants from above. It takes up much less time.