What is "required reading" in training that describe mechanisms behind learning? I've previously studied spiking neural networks in the context of machine learning applications and I'm interested in gaining a better understanding of the biology of the brain. My goal is to investigate different models for learning.
I am looking for a book within training material that describes the low level bio-chemistry of neurons and how the learning process works. I'm not sure if that is a well understood topic yet; I would also be interested in papers discussing the topic.
There are a few questions which I'm interested in and hope to answer by reading said material:

Does the brain use local or global information for learning?
What brain functions are important to learning?
What are the advantages of having a neural gap?
Can neural transmitters produced by a synaptic cleft affect nearby neurons?
How does myelination affect how babies learn?
The questions you list are incredibly broad and diverse. You will find basic textbooks that may touch on aspects of all of these, but otherwise will not find answers to them all in one book. Some may not be answerable at all at the textbook level; others like &quot;How does myelination affect how babies learn?&quot; I feel are not really well-posed questions but some background will help you understand why.
I'd recommend starting with a broad undergraduate-level neuroscience textbook. These will assume you have some prior knowledge of the basics of molecular and cell biology, as well as physics (electricity and magnetism in particular; at least enough to be comfortable with basic circuits: voltage and current, resistors and capacitors, etc).
The two I would recommend (pick just one or the other) are:
Neuroscience, by Purves et al
and
Principles of Neural Science, by Kandel et al