If your NPC was struck deaf after learning how to speak, they would not have a funny accent at all. But they would have trouble noticing when someone is talking, if they could not see them.
Decide when your NPC was deafened. If it was over a year the past, they probably learnt to read lips, but they may have trouble with characters with an unfamiliar non-human facial structure, or just big wiskers. Even with readable faces, it is impossible to tell 'B's from 'P's, 'Z's from 'S's, and so on. Would they be upfront and ask the PCs whether that name is with a 'keh' as in 'card' or 'guh' as in 'guard...ian?' Or would they just appear rude talking through people they don't see, and mispronouncing the unfamiliar names. If they are not telling, is it because of shame, or because it is too much trouble for some temp help that haven't maimed themselves for master the way NPC has? Will they be in the campaign long enough for the PCs to figure it out?
(I myself rarely share when my tinnitus acts up, because that is boring; if I'm bothering to read your face it is because I want to learn something new.)
Also consider deaf people are able to notice some forms of sound. If something heavy falls, that shakes the floor. Music with drums can likewise be felt. Many people who are legally deaf can hear some tones, just not enough to make out speech. What is the exact nature of the curse? How does it interact with magic and illusory sounds, if your setting has such?
Basically, like TookyG said, do some research. But this may help you start the mental research on deafness on your own.