The linguistic diversity of the Ottoman Empire was quite vast. Generally speaking, Turkish was an administrative language outside of Anatolia. Non-Turks would learn Turkish to interact with the imperial bureaucracy, which was pretty anemic and the empire often delegated out to local elites. The Ottomanist reforms of the Young Turks in 1907 never had a clear answer to the language issue. On one hand, modernizers sought to homogenize the empire and try to force a Turkification of language. This was challenged by more moderates among the CUP who favored an acceptance of multilingualism in exchange for the loyalty of Jewish and Arabic speakers to the empire. And of course there were those in between, Namik Kemal and Omer Naci, for example were two prominent Turks that blended Arabic and Persian idioms and phrasings into their speeches and writing. The First World War led to the victory of the Turkifiers.

The case of Lebanon is unique in that the French managed to carve out a quasi-dependency out of the Mount Lebanon region. This meant that not only was Turkish a language of state, but French as well (the French acted as an intercessor between the Ottoman government to the advantage of Maronite Christians). So if your grandfather was an urban dweller and of a relatively high social standing, knowledge of Turkish might have been useful. Of course, if he were drafted during the war, he might also have had to learn Turkish. Generally speaking, urban areas in empires tend to have a very high proportion of multilingualism.

Not a historian at all, but Turkish was not widely spoken outside of Anatolia at all during the Ottoman Empire, really. Arabic was still the dominant language used in most of the middle east, and that's reflected today. Even many Ottoman caliphs spoke Arabic as a secondary/tertiary language, like Mehmet the Conqueror.