As you might already know, the logo on the left of your site header is added from the theme. More information can be found in this article.
You can also put a logo to the right of your header, and it can be conveniently done from the site editor! Here's how it's done.
To add a logo to the right of the site header:
1. Upload your logo to the Media Library.
2. Go to the site editor and click Edit besides the site title on the upper left corner.
3. Tick the box for Display secondary logo.
4. Select the logo from the Media Library.
5. Set preferred property value for background-size and background-position.
6. Click Done Editing button.