If you would like to truncating Headline schema property output, there is a filter included in Schema plugin that will allow to do so. We’ve included two examples of how to truncate Headlines by words count, or number of characters.
Truncating Headlines by words count
You can add this code to your Theme’s functions.php file.
Truncating Headlines by characters count
You can add this code to your Theme’s functions.php file.
Note: This will only truncate headlines in schema.org markup output, and does not have effect on the actual post title on your WordPress site.