Demotic is using the hieroglyphic writing system. Unlike English for example where there is a letter for each sound (i.e alphabet), Egyptian writing system had some symbols that represent one sound (like English), other symbols that represent two sounds and others that represent 3 sounds and others (called determinative), didn't represent any sound at all but rather gives you a clue what the word means.
You might find demotic symbols that represent most of the Coptic alphabet (except some vowels) but that's not the whole writing system.
Anyway, I found many tables for you that show some of the demotic letters and their pronunciation. since I can't verify accuracy of any of the results, I will give you link to
search result so you can take what you feel is correct.
