Question

What is the subject of the following sentence?: John and I are shopping at the mall.

Answer 1

The subject is "John and I," which is a compound subject.

Explanation:

The subject in this sentence is a "compound subject."

Compound subjects are formed from two or more subjects joined by a coordinating conjunction (and, both, or, neither, nor).

When the conjunction is "and," the verb is plural

`color(white)(.....)` John and I `color(white)(...........)` are
(compound subject)  (plural verb)

You can find out more about compound subjects here:
http://examples.yourdictionary.com/compound-subject-examples.html