Well, there is no finite answer to "how often should I water my bonsai?" as you have to watch the plant and test the soil to see how damp it is. You should never let the woil dry out completely, nor should you overwater the plant as you will drown the roots. Just keep watch on the soil, when it starts to dry out a bit, give it some water.
You can test to see if the deep soil is dry/wet by pushing a wooden skewer into the soil. If the skewer is damp, then the tree does not yet need watering.
There are a plethora of bonsai books out there, and you can probably find some at your local library. Every good bonsai book has a chapter on watering. I believe that Scott has a section on watering in this website as well and here is another link:
Click on Bonsai basics.