How to Prune noble dendrobium?
No pruning required, cut down flowered stems as necessary

noble dendrobium · Dendrobium nobile
Also known as: noble rock orchid
Grow in epiphytic orchid compost and from late spring to summer, in partial shade with good ventilation, day temperatures between 18-25°C and night above 10°C, water freely adding orchid fertiliser every third watering and provide high humidity by misting twice daily. Keep in well lit conditions from autumn to early spring and keep dry in winter. See indoor orchid cultivation
No pruning required, cut down flowered stems as necessary