Den nobile and hybrids don't necessarily drop leaves during dormancy. You might notice the ones sold in shops that are loaded with flowers usually have full sets of leaves on all the pseudobulbs. These plants have been watered so they keep their leaves, and chilled so they flower.
Yamamoto Dendrobiums [had] detailed growing information on their site. This includes summer fertilizer management and winter temperature recommendations, both of which they say are very important for flowering. They recommend light winter watering, and not resuming heavy watering until new growth appears at the base.
Edit June 15 2020:
Yamamoto Dendrobiums in Japan hybridizes and produces a great number of these plants. Their Web site formerly had excellent growing information for hobbyists. Unfortunately it is no longer there. You can still look at the varieties they grow, and maybe see one very similar to yours.
I saved the page, and summarized it in a post in this thread:
Uncertain if Dendrobium is still alive
Yamamoto now has a
page showing how to force Dendrobium nobile for Christmas flowering in Japan's climate. There is a lot to learn from that page, but it is intended for growers who can artificially heat and cool their greenhouses during off seasons. Note they use coconut husk for growing medium, which many orchidists would say retains too much water for orchids. For many orchids that is correct, but this is a very thirsty orchid.
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