Does anybody know who wrote the book of Jonah?
What the SDABC says:
Although the book itself nowhere states that Jonah was the author, the traditional view has been that he was. Many modern scholars have favored a postexilic authorship though not necessarily denying the historicity of Jonah. However, the arguments they advance, such as the presence of Aramaisms, are inconclusive. The study of Ugaritic has demonstrated the antiquity of many forms and words that were formerly held to belong to a much later date (see on Ps. 2:12; see Vol. III, pp. 618, 619). The use of the third person is likewise an insufficient argument, inasmuch as not a few ancient writers, such as Xenophon, Caesar, and others employed this method. Bible writers, too, at times used this method (Isa. 7:3; 20:2; Jer. 20:1, 3; 26:7; Dan. 1:6–11, 17, 19, 21; Dan. 2:14–20; etc.; see on Ezra 7:28).