Hi @alonagomez,
With the core WordPress Job Manager plugin the only options are to apply either by sending an email or going to another link that you provide to apply.
You can make it so that users aren’t able to view the job postings without being logged in by changing the Job Visibility to limit it to certain signed in roles from the Admin page > Job Listings > Settings > Job Visibility.
You would need to use custom code or a different plugin to make it show Register to Apply for users that are logged out.
If you have the Applications plugin that does have the option to only allow logged in users to apply and will prompt them to login or create an account if they are logged out.
If you have any other questions, give us a shout!