What's the brix of a typical avocado?
The basic definition of Brix is grams sugar per 100 g solution. For an avocado, the FDA’s  nutrition data says that’s 8.5 °Bx.
The Brix scale is generally applied to solutions consisting mostly of sugar and water. That’s why it’s possible to use something like specific gravity or a refractometer to measure it. For solutions with other significant components, it’s not possible to use a refractometer or hydrometer to accurately measure Brix.