Hi peter.jak,
The Smart.DockingLayout doesn’t have a specific event for item focusing. However there are several solutions. One of which is to use the native document.activeElement to get the currently focused element on the page. You can combine that with a click event and you will have exactly what you need. Here’s how to do it:

 document.querySelector('smart-docking-layout').addEventListener('click', function() {
        if(document.activeElement) {

This code will log you the currently focused Smart.TabsWindow. From there you can get it’s id,name or any other property.
Another approach is to get all Smart.DockingLayout items via the getter items and cycle through them to find which one has the ‘active’ attribute, like so:

const items = document.querySelector('smart-docking-layout').items;
document.querySelector('smart-docking-layout').addEventListener('click', function() {
    console.log(items.find(item => item.hasAttribute('active')));

Best Regards,
Smart HTML Elements Team