To enable the WPBakery Page Builder for the portfolio posts, go to WPBakery Page Builder - Role Manager and under the user role set "Post types" to Custom.  Once set, a list of all the available post types will show up. Check the "portfolio" option.

More info: https://wpbakery.com/video-academy/use-wpbakery-page-builder-pages-posts-custom-posts-wordpress/