If I understand you correctly, It sounds like you should be adding this to your widget or theme.
I don't think adding a filter is what you want to do. Filters are used to modify data, an "action" would be better if you're trying to figure out when a specific widget area is requested. But, this would not be useful in this regard because it's also called on the ACP Widget page.
What you probably want to do is use the existing "filter:widget.render:widgetname" hook,
plugins.fireHook('filter:widget.render:' + widget.widget, {
uid: uid,
area: area,
data: widget.data
}
The area that is passed has area.template already.