I have ground ginger. How much do I use to replace for 1 Tbsp. of fresh ginger?

Common proportion for spices is 1 tbsp fresh = 1 tsp dried (and vice versa).
If you like ginger, start with the 1 tsp.
if you're cautious or not sure how much ginger taste you want, start with 1/2 tsp dried, taste the mixed or cooked dish and - if needed - add more.