Can you tell what loss of use is due to never getting cartilage back if I had knee surgery for torn meniscus?

If you are asking what remaining loss of use you will have after surgery, no one can answer that. If you are stating that you already had surgery, then your doctor can state what remaining degree of loss of use you have. You state that you are working in a physically demanding job, so it sounds like you don't have a loss of use: you are using the knee without restriction (or so it would seem). If you are asking for a definition of loss of use, it is when a doctor determines that you have some sort of limitation or restriction which prohibits you from having full use of the knee.