Yours is an excellent question, as there seem to be few works (either books or scholarly articles) that deal with Johannes Eck exclusively, although he is discussed (though not exclusively) in several books dealing with the reformation in Germany.  There is a dissertation in English, written in 1967 by Walter Lane Moore, titled Between Mani and Pelagius: Predestination and Justification in the Early Writings of Johannes Eck.  Although I don't think it was ever published, it may be available from the Harvard Divinity School since universities do keep copies of the dissertations written by their graduate students.  Of course, if they don't make copies available, you may have to physically go to the Harvard Divinity School library to read it.  Another work that deals with Eck is T. Wiedemann's Dr. Johann Eck: Professor der Theologie an der Universitat Ingolstadt (Regenburg, 1865).  Again though, given its publication date, this book may be nearly impossible to find.  Of the books that mention Eck among the other Reformers, the one that seems to delve more deeply into his role as Luther's opponent is The Primacy of the Postils: Catholics, Protestants, and the Dissemination of Ideas in Early Modern Germany by John M. Frymire (Brill, 1987).  This one is available, although it is pricey.  You could try Google Books to read the section on Eck without having to get the entire book.

Thank you for your extremely helpful reply. I do have Wiedemann's biography, a Nadu Press reprint  (2011)-- in deutsche Schrift (Fraktur)!  The Fyrmire book will be very useful, I'm sure. Perhaps I can buy a relevant chapter or two from Brill.  Frymire's research appears to be a great find.  I'll have to check on the Harvard library.  If anyone has a used copy of the Frymire book on The Primacy of the Postils to sell, I would be interested. Of course, any additional suggestions would be appreciated.  It does seem like I'll have to delve into various works on the Reformation and Reformation period.

It probably doesn't contain anything new to you, but he is discussed in Roland H. Bainton's "Here I Stand - A Life of Martin Luther".  There's ten solid pages on him and about fifteen further references to him later in the text.  Published in about 1950 and widely available in a variety of editions, I believe.

Thank you Kal for your reply. The Bainton work is outstanding, yet it is one of the reasons I want to do research on J. Eck. Bainton's focus is on Luther as the Reformation's  epic hero. I'd like to explore what insights might derive from looking at Eck from an alternative point of view.   For example, I want to investigate whether more can be understood about Eck's role in the development of the papal bull "Exsurge Domine" than  "Here I Stand" provides . Surely after more than 50 years, additional research and a fresh point of view may be productive.  Thanks again!