Question

be supposed to be和be supposed to do有什么区别

Answer 1

前者be数与系动词，后面可接名词、动名词、形容词、过去分词作表语；后者do就是代指动词原形

Answer 2

be supposed to do sth为一常用短语，如后面没动词，就用be supposed to be
如：
You are supposed to come here on time.
You are supposed to be in the classroom now.

Answer 3

be此处可看做是动词原形do。