Because there are so few words of Khuzdul, we largely have to turn to other languages for comparative analysis. That includes languages in Middle-earth and in our own "Primary World", as Tolkien called it. A number of people have paved the way in providing information and analysis of the other languages in Middle-earth. To understand Semitic languages such as Hebrew and Arabic, to which Khuzdul is said to be similar, I turned to quite a few books and papers, online and hard-copy, as well as websites for general reference. The following list are the resources that I found especially helpful in learning about all of these languages, both in Middle-earth and in the real world.
The Lord of the Rings - The original story itself. I would be remiss if I did not include this in my list of references! Appendix E, found at the end of "The Return of the King", was of particular value.
The Histories of Middle-earth (series) - J.R.R. Tolkien's son, Christopher Tolkien, has published a series of books laying out much of the development of the stories of Middle-earth, as well as some of the writings about the languages and cultures. It is invaluable to understanding the works of Tolkien and the processby which he made them. I won't link every one here, but the volumes that were of particular use t me were "The Peoples of Middle-earth", "The War of the Jewels", "The Treason of Isengard", and "Sauron Defeated".
The Silmarillion - An account of the early ages of Middle-earth. It contains, for this project, a small bit of useful linguistic information.
The Unfinished Tales - Additional information about the ages of Middle-earth, and a little information useful for Khuzdul.
The Lord of the Rings: A Reader's Companion - Has information about the process of writing "The Lord of the Rings", and as part of that includes some information about Khuzdul as well.
Ardalambion - A well known website run by Helge Fauskanger, it contains a comprehensive overview of all the languages Tolkien created. In particular, there are sections on Khudzul, Adunaic, and Quenya. Helge provides a course on Quenya as well, and that was very helpful to quickly understand the similarities between Adunaic and Quenya, such that I could see where differences between Khuzdul and Adunaic might lie. The article on Khuzdul was instrumental to helping me understand the language back when I first started on my journey in "Tolkienian linguistics".
An Analysis of Dwarvish - Magnus Åberg wrote the first (only?) article on Khuzdul that extensively compares it with Hebrew. Magnus took a class in Biblical Hebrew at one point, and used "Introduction to Biblical Hebrew" by Thomas O. Lambdin. It was from Magnus that I learned of the book, and proceeded to buy and use it myself. I had extensive conversations with Magnus regarding Khuzdul, and several of the theories he presents came out of those conversations. Our ideas are still not very far apart, even though I have updated a few of my thoughts. Still, had it not been for my Swedish friend, this work would not be possible.
Elfling Email List - This email list is for the discussion of Tolkien's languages. This served as another point of contact to discuss ideas about Khuzdul and linguistics when I was first learning. It's not as active these days, but the archives are availble for search and are worthwhile.
Elvish Linguistics Fellowship - Homepage of the group that publishes the papers of J.R.R. Tolkien. It includes another email discussion list as well as the Parma Eldalamberon and Vinyar Tengwar publications, which provided at least some information about Khuzdul not found in the primary sources. There may be additional notes on Khuzdul that have not been published yet. If so, this will be the place to find them.
Lalaith's Guide to Adûnaic Grammar - This article presents Adunaic, in a fashion comparable to Ardalambion, but presents things slightly different and with a few alternate theories. Very worthwhile in understanding the language.
"Primary World" Languages
Introduction to Biblical Hebrew - Written by Thomas O. Lambdin, Professor Emeritus of Semitic Languages at Harvard University, this book makes liberal use of English transliteration. This is perfect for someone like me who wanted to understand the structures of Hebrew (to compare with Khuzdul), but didn't want or need to actually learn the Hebrew script. Lambdin does a great job of thoroughly presenting the language.
An Introduction to Koranic and Classical Arabic - The author is Wheeler M. Thackston, and like Lambdin, he uses English transliteration to present his grammar of the Classical Arabic language. Again, this is invaluable when speaking and reading Arabic is not your ultimate goal. His grammar is quite easy to understand, perhaps even more so than Lambdin's, so it might be a better place to start learning about Semitic languages. You can also find a PDF version of the book here.
Arabic Online - A well written, easy to follow grammar of the Arabic language. It covers both Classical and Modern Standard Arabic. In particular, I found the sections on the differences between active and stative verbs useful. The explanations of the differences between using the perfect, imperfect, and active participle was also very helpful.
Wikipedia - No, really! The language and linguistics pages on Wikipedia are actually of decent quality. They aren't perfect, but as general references for a project like this, Wikipedia can be quite helpful. No, I wouldn't use it as a sole reference in a scholarly article, but for getting a general sense of linguistic information to help in a largely creative project like this, absolutely. Where needed, I generally backed up what I found on Wikipedia with information from other sources as well. Even if exacting precision wasn't needed, knowing that the articles were at least in the ballpark was helpful. Here are the pages I referred to the most:
The Zompist Bulletin Board - This forum is dedicated to the hobby of constructed languages, or "conlanging" as it is known. The feedback can sometimes be harsh due to brutal honesty, but I have found a great amount of linguistic knowledge here. If you are willing to do some reading and learning, this is a great place to learn how to create a quality language or language family. My knowledge of linguistics is far greater as a result of having been a member for several years.