The second midterm will cover the content from Lecture 14 until Lecture 21. Please see the lecture log here.
This corresponds to the following chapters and sections of the book

Kenneth H. Rosen: Discrete Mathematics and Its Applications, McGraw-Hill, 7th edition

– Counting (Ch. 6, Sections 6.1-6.5)
– Discrete Probability (Ch. 7, Section 7.1)