What part of the Bible did Joshua write?

Answer 1

The book of Joshua itself attests to the authorship by him in Chapter 24.

26And Joshua wrote these words in the book of the law of God, and took a great stone, and set it up there under an oak, that was by the sanctuary of the LORD.

All other internal evidences and uniform tradition point to Joshua as the author with only minor later editing.

Answer 2

Tradition has it that Joshua wrote the Book of Joshua.

On the other hand, there is no evidence, internal to the Book of Joshua or external, that supports the tradition that it was written by Joshua. The book was written in a relatively late form of Hebrew and is too well integrated with the remainder of the Deuteronomic history (Books of Joshua, Judges, 1 and 2 Samuel and 1 and 2 Kings) to be likely to have a different author than those books.