How much pedialyte should i give to my 10 month old son? (his pediatrician advised that he take some, but he didn't prescribe a dosage.)

It depends: It depends on the problem. If your son has gastroenteritis ('stomach flu'), you need to keep offering Pedialyte in small frequent amounts to replace your son's losses from vomiting/diarrhea.

Pedialyte Guide: Pedialyte is great for short term (24 hours) hydration for children. A general guide is what your child takes normally at this age. Most 10 months old if they were exclusively breastfed would take 3-4 bottles a day (7-8 ounces per bottle) to give you a range. Make sure you call Pediatrician back if baby stops drinking or starts having fever, vomiting or diarrhea.

Varies: Pedialyte is a balanced way to get fluids/electrolytes into a kid having problems with normal intake.They need to take in enough to pee every 6 hrs, which will very by their weight and other sources of intake.Applesauce/Popsicles, soup, etc all provide fluid value, so no "dose" for pedialyte will be right for everyone.