Finding the Email header in Gmail

Problem/Question

How do I find the email header in Gmail?

Overview

Open header in reply, and then copy it.

Solution

1) Open up the email you want to get the headers of. 

2) Click the "more" caret next to the reply button.

3) Click on "Show original"

4) Copy all the text that shows up on the page, this is the email header. 

Notes:
You may have to scroll down to select all the text on the page that lists the email header.

Google has a guide located at: 
https://support.google.com/mail/answer/22454?hl=en