You can create your layout for every post type like: pages, posts and also Portfolio in Elementor by clicking on Edit with Elementor button in your page.
If you don't see that button in your Portfolio page, you have to activate Elementor for Portfolio custom post type.
In order to activate Elementor for Portfolio post type:
1. From WordPress left dashboard menu, click on Elementor.
2. In General tab, make sure you've checked the Portfolios in Post types option.
3. Save changes and now you can see the Edit with Elementor button for your Portfolio pages.