how to propogate Forsythiax intermedia

Easiest way is layering - peg a few shoots down either into pots or the soil, wait for roots (if you're lucky, by next spring, if not by the autumn) and then sever from the parent plant.

so it would look like a bamboo root with roots coming off instead of shoots?

x x

Well the roots will appear on the bit that's buried - you may still have growth continuing along the rest of the shoot both sides.

You could also try heel cuttings, but Bamboos method would produce a reasonable sized shrub quicker.