"Wanasoma kitabu changu."

Translation: They read my book.

[FubbiKenan]

Originally from Arabic word كِتاب (kitab) for book. Hindi also has the same Arabic word for book किताब.

[Drasher]

Would this mean a book that the speaker wrote, as jt usually does in English, or just one that they happen to own?

[ElMeuNom]

I think it could be either, just like the English sentence is ambiguous.

[thechangeroots]

Why is it changu instead of yangu? They both seem to mean my/mine, right?

[ElMeuNom]

Noun class. Ki/Vi nouns take changu in the singular (chake, chako, etc.) and vyangu in plural (vyake, vyako, etc.) Yangu (yake, yako, etc.) is used for M/Mi and Ji/Ma in the plural and N/N in the singular.