How do I strain ginger powder to make ginger tea?
I think, even though it’s way subjective, the best way to make ginger tea/(infusion actually) is to boil the fresh ginger in hot water for 4-5 minutes, and discard the ginger. 

So modifying this recipe, and adapting for ginger powder, you should boil the ginger powder for some time and then filter using a coffee filter. However you should try to find the optimum time here, I think it will be less than the time needed for fresh ginger, as the powdered ginger will have waaay more surface area than the fresh ginger.