What illness does my cat have?

My cat has been coughing and hacking, recent dramatic weight loss, wheezing, and lethargy. What does the X-ray attached appear to indicate what he has going on with him??

Hello! - are you checking up on your vets, or are you testing me?  The traditional convention for second opinions is not perfect, but makes sense in this scenario; one vet has presumably listened to your cats' chest, seen them breathe, examined them, ordered the tests they wanted to see and evaluated them.  They are in a much better place to comment on what is wrong with your cat, than an (other)? Non specialist vet who has a list of symptoms and an x-ray.   It is therefore worth having a think about what has led you to show the radiographs to me - should you trust my opinion above your vets' if I gave it to you?  Or will it simply muddy the waters?  For this reason, the standard and accepted route for diagnosis and second opinion is to go to a specialist in that area, or in radiography, who is a specialist because their opinion absolutely carries authority over that of a generalist.  Otherwise, where any differences apply, they are mostly unhelpful and therefore we do not give second opinions on this site.  Most vets, interestingly, love to send cases for second opinions because we learn from the process, so if you wish to then you should ask.

I have now looked that the radiograph, which is rather dramatic.  I would be interested in hearing what is diagnosed, if you would like to tell us.  I'm not surprised to hear that your cat is not breathing well, and I would be interested to see the DV view, in particular to further assess the diaphragm; however, I must repeat that we are not allowed to give second opinions on this site so it would be for my own interest.   Best of luck getting to the bottom of this case all the best to yourself and the patient.