I think Kia means "that." In previous examples, the Kia was put in front on the noun, but in this instance, it is out after. In the same sentence, we see that "này" was put after "mug" to indicate "this mug."
Yes, accents are all important in Vietnamese. If you practice the first alphabet unit, it goes over the difference between 'ca' and 'cá' quite a lot. This is the same for any other word - the wrong accent means the wrong tone which is a different word.