How many milligrams of oxytocin is released in the brain from the result of a hug? If that can be measured? Does anyone know?

Difficult to measure in brain--you'd have to collect cerebrospinal fluid, which is a very invasive procedure--as anybody who's ever had a spinal tap will tell you. But it's recently been found that a simple blood sample can give you a reasonable idea--since there's leakage from CSF into blood (and this can vary depending on what is trying to measure), the levels in blood reflect what's going on in the brain. Blood levels are uniformly lower than in CSF, but they've been found to correlate, so one can get a rough idea.

https://med.stanford.edu/news/all-news/2014/11/oxy...