You have to get familiar with template hierarchy to understand in which template WordPress will display your custom post type. If you have sample custom post type named event with title Lorem ipsum, WordPress will watch for this files in that order in your theme to display such a custom post type:
single-$post_type-$slug.phpfor our case it will be
single-event-lorem-ipsum.phpsingle-$post_type.phpfor our case it will besingle-event.phpsingle.phpsingluar.phpindex.php
If WordPress will not find first of the file from list it will be looking for second and so on.
Most of the themes has single.php file and probably your custom post type will be displayed by this template. Good practice would be to create separate template file for custom post type, probably you want to display it display differently than others post, named single-event.php. For start I would copy single.php content, paste it to single-event.php file and add there your ACF code.