Can Fuji apples do well under these conditions:- https://en.climate-data.org/africa/kenya/trans-nzoia/kitale-919/#climate-graph Do i have the chill hours required my region? What is the recommended plant spacing for commercial growing?
I'm sorry, but it doesn't seem that it even approaches the chill temperature requirement, or chill hours.
The bottom of this article will recommend cultivars that do not have a strict chill requirement: https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-8/zone-8-apple-trees.htm
This collection of articles will offer more information on growing apples: https://www.gardeningknowhow.com/category/edible/fruits/apples
What is it and how do we get rid of it. I was going to spray it with water, vinegar and dish soap
Without a photo, I'd say it could be mealy bugs. They leave white cottony patches on leaves and stems. Powdery mildew is common with Fuji apple trees, but that would be more on the leaves. There also are wooly aphids which will graze on leaves, stems, branches and even bark.