You may find these codes in /components/com_easysocial/themes/wireframe/conversations/default/actions.php

Hello Mark,
Thank you for your reply.

How can I retrieve the ID of the selected member in the left column (the one whose messages are displayed)

Best regards.

Eric

How we retrieve those conversation id is :

1. render the conversation id in the HTML code
JoomlaFolder/components/com_easysocial/themes/wireframe/conversations/default/lists.php
You can refer on my first attached screenshot below.

2. Use jQuery to find this data-id element
JoomlaFolder/media/com_easysocial/scripts/site/conversations/item.js
You can refer on my second attached screenshot below.

3. Call the ajax function through just now that Javascript.
JoomlaFolder/components/com_easysocial/views/conversations/view.ajax.php (getConversation method)