Question 1. is, strictly speaking, ungrammatical, and vague in most interpretations. If by graph algebra you mean algebraic graph theory,
then the question is hopelessly broad. If by question 1. you mean
``What is the relationship between graph algebras (in the sense of Lovász) and quantum graphs (also in the sense of Lovász),
then the question is extremely specific and easy to answer: a quantum
graph (in the sense of Lovász) is an element of a graph algebra
(in the sense of Lovász). A definition of both these notions
is given in e.g.
Hatami, H. and Norine, S.: Undecidability of linear inequalities in graph homomorphism densities. Journal of the American Mathematical Society, Vol. 24, No. 2 (2011), p.547--565
which would also be my answer to Question 2.
This is a good article to start,
rich in mathematical context
(e.g. Artin's solution of Hilbert's seventeenth problem).