In your browser, right click on the asset, and “Inspect Element” (or press F12).
You should see a window or inspector pane show, look for the “Network” tab.

If you see a ‘disable cache’ checkbox, check that and then reload the image.

This will list out the images loaded, and if cached in the Status/Size columns.

If you click on the image you’re loading from the Spaces CDB, it will list out the headers sent, including where it was served from.