In the Forgotten Vale, on the quest of making the journey to each way shrine, there is a boss fight involves two dragons, Voslaarum & Naaslaarum, over a frozen lake. While the player is walking/running over the lake, the dragons are supposed to appear but, for me, they do not. I've tried loading an earlier save that is in the Vale but the same thing happens. I've ran all over the place with the same results. My next earlier save is about an hour prior to entering the Vale and I'd prefer not to go through an hour of stuff I've already done just to see if the dragons appear.

Is there a console command I can use to activate the trigger for them?

Edit:
I found the cause: the player needs to complete the portion of Skyrim's main quest that triggers the random dragon encounters. If the player doesn't do this, then these two dragons will not appear. If you are already past this section of the Vale, then you can always come back to fight the two dragons.