I think it's mostly just knowing your hair and it can take a some careful observation to figure out.
I seem to shed a lot. I rarely comb my hair, I mostly finger comb it into a loose bun or just finger comb the curls and wear it loose. When I do comb I have a literal handful of hair. Each strand is shed with a little bulb at the end. I actually untangled and counted the shed hairs a few times. They come to about 40 hairs. I comb my hair maybe twice a week, right after washing.