I want to leave the right side of each page blank for taking notes.
A simple way is to use one-column layout instead and change the right margin, but using geometry package will affect current template. I'm using
\documentclass[journal,onecolumn,]{IEEEtran}
After applying geometry package, other margins are changed, ruining the template.
I also tried \addtolength{\rightmargin}{.3\paperwidth} without using geometry package, but it doesn't change the margin at all.
I also tried multicols, but it only leaves the right column of the last page blank.
The template I used can be found here.
Related questions:

geometry? Please add a minimal working example (MWE) of how you ruin the template withgeometryand explain clearly and exactly what you need instead. By the way, theIEEEtranclass was designed to submit articles as is, not to make your own customs layout to take notes. I would start with a general purpose class asarticleor even thetufteclass, that by default left a huge right margin. – Fran Nov 21 '18 at 22:24