Jinnicky the Red Jinn makes a cameo in which twenty-ninth book by L. Frank Baum and his successors?
Jinnicky the Red Jinn:  (He makes a cameo appearance in "The Wishing Horse of Oz", and he is the principal pre-existing character in Thompson's sub-canonical penultimate Oz book, "Yankee in Oz"). The Wishing Horse of Oz: The Wishing Horse of Oz (1935) is the twenty-ninth in the series of Oz books created by L. Frank Baum and his successors, and the fifteenth written by Ruth Plumly Thompson.
The Wishing Horse of Oz