Car-uh (the most normal sounding, and perceived named pronunciation) Kar-uh (would technically make the most sense, considering their name is short for character, sounds the weirdest) Char-uh (the most accurate to the spelling of the name)
Chara is a Greek feminine name pronounced “kahr-ah”. The hard c sound comes from the Greek letter chi. It looks like an X but it’s pronounced like the ch in anarchy. That’s why Christmas is shortened to Xmas.
Chara, Frisk, Asriel and Gaster have the ability to exist in the inexistence. After erasing the universe (I don't know if Chata can erase any universe besides Undertale), the game turns into a black screen with tge sound of wind, and Chara speaks to you without any physical form.