The agent page  is displayed by the file single-estate_agent.php . In this page there are 3 main components:

The agent details which is located in templates/agentdetails.php

Here we display the agent details like phone, skype etc. The details are saved as custom meta for the estate_agent custom post type. They are retried using get_post_meta

$agent_phone = esc_html( get_post_meta($post->ID, 'agent_phone', true) );

The contact form located in templates/agent_contact.php

In this page we check if the the contact form is a contact 7 one and we display the right contact form. The WPResidence contact form email is sent via ajax when the button with id=”agent_submit” is pressed.

The Contact 7 buttons are displayed via code like

do_shortcode($contact_form_7_agent)

The agent listings code is located in  templates/agent_listings.php

In this file we do a wp_query that search for all properties assingned to the respective agent. The key element for this query is this portion of the $args array

'meta_query' => array(
array(
'key' => 'property_agent',
'value' => $agent_id,
)
)

If you need additiona details about how this is done you should read the meta query section from official documentation : https://codex.wordpress.org/Class_Reference/WP_Query