It would depend on the context! If someone was talking about garden soil, I might assume that we were speaking of amounts or percentages of chalk in the soil. In a school situation, I would assume that the person was asking how many pieces of chalk I have.
Hey Akasaka, you shouldn't say "do you have much chalk?", instead say "do you have much chalk left?", which is the same as "do you have a lot of chalk left?". "Much chalk" could mean either many pieces or a whole amount.
"Do you have lots of chalk?"
"Do you have many pieces of chalk?" "Do you have large amounts of chalk?"
"Do you have a large number of pieces of chalk?"
"Do you have numerous pieces of chalk?" "Do you have plenty of chalk?" "Do you have a good supply of chalk?"
If you're talking about pieces of chalk in a classroom, asking if you have "much" chalk would, presumably, be asking if you have a supply of pieces of chalk.
As Joelline indicated, please don't assume that we know what chalk you're talking about - the sentences that I've bolded could, indeed, be talking about having chalk in your garden soil or in bags in your garden shed. We always need to know what the context is.