See q2apro-onsitenotifications-layer.php
$this->content['loggedin']['suffix'] = @$this->content['loggedin']['suffix'].' <a class="qa-history-new-event-link" title="'.$tooltip.'"><span class="notifybub ntfy-event-nill">'.qa_opt('q2apro_onsitenotifications_nill').'</span></a>';
With the snow theme there is no avatar on top. It seems you are using a custom theme. Check out its custom code.
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In general for others who want to change any CSS or alike:
This is the HTML:
<span class="qa-logged-in-pad">
<a class="qa-history-new-event-link"><span class="notifybub qa-history-event-nill">N</span></a>
</span>
If you click on the "N" (.notifybub), jquery does the ajax request and appends it to the anchor (see script.js):
$(".qa-history-new-event-link").append(data);
Where "data" contains the "<div id="nfyWrap" class="nfyWrap">" plus all the user events.
The regarding CSS is determined in styles.css.