All of the characters in the ASCII character code are listed in the table at http://www.dgp.toronto.edu/~ajr/104/diary/01/ascii.html
I did accept "space" or specific control-characters for part 'a', although I think it's pretty clear to say that these aren't actually characters, especially the space.
I worried that part 'b' might give an unfair advantage to speakers of Chinese, Japanese, or Korean, who are used to thinking of glyphs in those written languages as "characters" -- any character from any of these languages would be a good answer to part 'b'. Indeed, several students used this. But after reading all of the answers, I don't think that this actually turned out to be an unfair advantage. I did in one or two cases give the points for part 'b' to people who wrote "Chinese characters", even though that wasn't actually an example character, in recognition of the fact that some students would know some Chinese characters and some wouldn't.
Another concern I had before grading was if someone would think of a glyph which they didn't know was in the ASCII character set, but it happens to be, but there's no way they could have known this (without memorizing the whole table, which is silly). I also think that that didn't actually turn out to be a problem here. In almost all cases where someone mentioned a character for part 'b' which was actually in the ASCII character code, it was a character which you have used in doing your assignments in this course. So the misunderstanding was indeed about what the ASCII character code covers, which is what was supposed to be being tested here.
So, what good answers are there for part 'b', if you don't know Chinese or Japanese or Korean? Lots of answers. Glyphs from any language other than English, including accented characters from other Latin-letter-based languages (e.g. French). Various symbols you've seen -- some people used an infinity symbol, and some mentioned symbols which we've specifically discussed aren't in the ASCII character set and thus we need some other way to type them in our spreadsheet formulas and computer programs, such as "≤" and "÷". All of the examples where we've used embedded images for a character, such as in question 9 of this same exam. And, I also accepted things like a happy-face symbol and other things which people think of as embedded in text due to their use in "chat" programs these days.