你上哪儿=你去哪儿=where are you going? 课 is NOT a place so you cannot use 你上哪儿 as sample of this but you can say 我上图书馆 which means 我去图书馆 and so as 我上那边 我上读书 is invalid, please try another one.

你上哪儿 = 你去哪儿? yes A. 我上图书馆。 B. 我上那边。 C.我去上课. D.我去读书.

A. 我上课. 上课is a word, u can't change it B. 我上图书馆。 but in BCD,"上"or"去"is a verb,and 图书馆、那边refer to a place,noun or adv,so “去”=“上” D. 我上那边。 C. 我上读书。 in C，读书is a verb,like A,you can only say“去”，去上课，去读书

I don't think "我上图书馆" is quite wrong... Maybe you can say "我上课" but it's better to add "去",because you're GOING to class."上课" is a expression. "我上那边" is right. "我上读书" is totally wrong. Because "你上哪儿" means "WHERE are you going" ^-^

here, 你上哪儿 = 你去哪儿. It is the same as, "Where are you headed?"; "Where are you going?" in the situation, “上”is a vt ,the same as “去”,but when you answer ,just with only a place So , you can answer A. 我上图书馆。 B. 我上那边。 C.我去上课. D.我去读书.