Checking abv after fermentation

I started my first batch of mead on 7/29. It’s a cyser with apple juice, and all other mead ingredients. I do not own a hydrometer yet. Is there a way to check the abv of the brew after it’s done fermenting?

Secondary question. I’ll be adding the last of the yeast nutrient tonight when I get home from work. If the mead is still bubbling/foaming should I wait to add the nutrient till it stops or is it safe to go ahead and add it?