Showing all specifications even there is not job

You can show all the options for a job specification in the job filters with the below code snippets.

function awsm_filter_spec_terms_custom_args( $terms_args ) {
    $terms_args['hide_empty'] = false;
    return $terms_args;
}
add_filter( 'awsm_filter_spec_terms_args', 'awsm_filter_spec_terms_custom_args' );

External Resources
https://wp-content.co/add-custom-code-to-your-wordpress-websites/