How do I activate the dragons den side quest in Pokemon Soul Silver?

There's no side quest called "Dragon's Den" in Pokemon Soul Silver. It's likely you're thinking of a different game or a different quest.

Could you provide more context? Perhaps:

* What is the goal of the quest you're looking for? (e.g., catching a specific Dragon-type Pokemon, obtaining a special item)

* Where do you think it might take place? (e.g., a cave, a specific town)

* What triggers the quest? (e.g., talking to a specific NPC, reaching a certain point in the main story)

With more details, I can better understand your request and help you find the quest you're looking for!