Welcome to the Netlify Forums This is a great question. Currently, there is no way for you to check which site is using more bandwidth on your end. We have an issue for this, and one of the Netlify teams is working on changing this. For now, we can look into this on our end for you.
Can you please share your Netlify site name? This will allow us to dig in further. Thanks!
So I have taken a look, and it looks like thirsty-lalande-3d7a33 is the site using your bandwidth, specifically for this image. My suggestion would be starting by making this smaller to reduce bandwidth.