Can you suggest any book or lecture notes that explain the theory of Stohr-Voloch?
Regards
I am not sure I am the right person to answer, as I can't judge the exposition since I kind of know the subject already. I think the original paper is quite readable. For books, you can look at:
Algebraic Curves over a Finite Field, J.W.P. Hirschfeld, G. Korchmáros, F. Torres, PUP
Algebraic Functions and Projective Curves, David Goldschmidt, Springer.
If you have any specific question, ask here on MO.