Question

Draw a hut under a tree.
which is subject and predicate

Answer 1

http://www.learnamericanenglishonline.com/Red%20Level/R4%20Commands.html

This is a command. The subject is "understood" (read the webpage) and not written, so all of the written sentence is the predicate.

Answer 2

Which is the subject in the sentence draw a tree under a
tree

Answer 3

In that hut lived an old woman subject or predicate