How you add schema markup to your WordPress (WP) site will depend on whether you’re adding it to one page at a time, or doing a large-scale implementation. For large scale implementations, I recommend you work with a website developer who can add JSON-LD to the header section of your WP theme.
If you’re implementing schema markup on one page at a time, you can easily paste your code where you want it whether you use the block editor (Gutenberg) or the classic editor. In the block editor, click the three stacked dots on the upper right corner of the editor, and select code editor from the navigation that appears.
In the classic editor, toggle the view by clicking on the text tab.
Paste your code where you want it to appear and save your changes.