I’m reading about both epistemic logic and deontic logic and I am trying to understand what is the relationship between them. Is epistemic logic considered a type of modal logic?
Both deontic and epistemic logic are considered to be modal logics, arising from special interpretations of modal operators. Also, there are some language extensions of basic modal logics that are motivated by the respective interpretations, e.g. those with group epistemic modalities. Take a look at van Benthem's Modal Logic for Open Minds, for example, if you want to learn more about the general perspective vs. special interpretations and extensions.