Might be wide both mark from what you were asking , but AS had already stated there is no published data regarding the volumes of dox and it's effectiveness. Even though it's been around for 50 years.
The original p1b design with it's straight dox comparison could have provided some data but that's all changed now. (After the famous whaler spork brawl)
"Doxorubicin attacks all cells . But do all cancer cells contain FAP and so does targeted Doxorubicin attack all cancerous cells or only some of them?"
You've missed the point a bit here, do some reading.
Dox is inert until it encounters the fap rich environment of a tumour it is then cleaved where it becomes active. Crucially only at the site of the tumour where it sets to work killing the cells.
I'm no scientist but I'd imagine some would escape the tumour environment but it's half life means once it's activated it does the damage to the tumour and hence no real side effects are seen.