How many calories does 8oz of de-fatted homemade chicken broth contain?

Homemade chicken stock can have a variety of densities, from being almost thick enough to cut into cubes at room temperature, to being a very thin broth, depending on the volume of chicken solids you used in making it, and how much you reduced it. The variation is mostly going to be from gelatin.

With this level of variability, there is no reasonable way to give you a specific calorie estimate.

Live Strong estimates 75 calories per cup, but don't detail the nature of the stock they are assessing. Still, this probably a good baseline; your product is probably in the 50-100 calorie per cup range.

I don't think this is mathematically possible. An entire 4.5 pound raw chicken only has about 1000 calories. Add another 200 calories for the carrots, celery and onion, and you get an absolute maximum of 1200 calories for the entire pot. If you use this to make 16 cups of stock, that means the absolute maximum calories a cup of stock could contain is 75.
Now you have to subtract all the calories from the stuff you take out of the pot. If you chill it to solidify the fat and remove all of it (about 65 grams, some of which is probably still in the chicken skin, which you also took out), then you have removed about 585 calories of fat, leaving about 615 calories in the whole pot (38 calories per cup if you made 16 cups) and that's BEFORE you subtract the calories remaining in the chicken body and vegetables that you took out of the pot. I have no idea how many calories the boiled chicken and vegetables contain, but I would estimate that we are talking about a virtually insignificant number of calories remaining in the stock. Maybe 15 calories per cup, probably less. If you make "clarified" stock (which I don't), it's probably a single digit number of calories remaining in each serving of finished stock.