The only record I have is this death certificate, and because I can find nothing about any town called "Zahila", I assume it must be a mis-dictation or a nonstandard transliteration from Arabic.
My great-great grandfather would have been born in modern-day Syria or Lebanon during Ottoman rule. I believe he was a Syriac/Assyrian Christian, although I'm not certain. Both his parents are also listed as being born in that place.
Does anybody with a knowledge of Arabic or Ottoman-era Syria know of such a place, or what it may be known-as today?
IMHO, the most likely candidate is Zahlé in Lebanon.
In case you're wondering what happened to the i in Zahila, in colloquial Arabic, short vowels are often dropped and sometimes even rearranged. Also final a (written with the Arabic letter ة = tāʾ marbūṭa) is often transliterated as e or eh.
It sounds very like Zahlé, a city of eastern Lebanon with a substantial Syriac minority. I've never encountered this spelling, but I imagine it was an official's attempt to spell an unfamiliar word: names too were often altered in this way, becoming part of the official record. No other candidates spring to mind.
It sounds like it might be Zahle, a Lebanese town.