How can i keep my window open and look at my email for a code

Hit the minimize button at the upper left corner of your screen.

How do i keep my window open on my s9 smartphone while receiving an email code from IRS

I domt know how to keep my email open while trying to get my code for filing taxes

Are you filing from a phone or computer?

If on a computer you can open a different tab. 

If on your phone, you can pull the code from your email from the notification bar at the top of your phone, so you do not have to close the program.