DDD with EF Core(DTO, Business, Etc)

I'm trying to get into Design Patterns and REST API's, and for a project i use Entity Framework Core with:
- Repository pattern
- Unit of work

Some things that are really foggy for me:
- Data validation, where should this be done?
- Events? Example: When user is registrered i want to send them an email.
- Should business layer take DTO or Domain models?
- What should go into the controller?

I know these things also depends on the developer, but what's the best/"original" way to go about this.