Anne is simply saying that she read Rod's Cavalier Health twitter comment about being aware of diabetes, and she is asking if there is a shortcut to learning about all of the various topics in veterinary medicine, particularly those specific to Cavaliers. She did not say that Ella has symptoms of diabetes or that she fears that Ella has diabetes - she is just asking about ways to become educated.
Unfortunately, there is no shortcut to learning. Time (to study) and experience are essential to learning. As example, I have a serious library of vet textbooks (which are not cheap and have to be replaced as new editions come out) that I've been reading for twenty years. I've also owned a larger number of dogs over that time than most pet owners in addition to working with fosters, so I've had to learn more than average as I've dealt with diseases in those dogs under my care. Some people want to dig deep into the nitty-gritty and others don't and would rather follow their vets' advice without understanding the details - it's a personal preference and there is no wrong or right. I have a personal interest and I also had a background (long ago) in human medicine so I had a foundation with which to start as far as understanding jargon, etc. I've made a deliberate decision to invest a huge amount of my personal time into learning over many years because I have a passion for this subject.
It's best to start with what affects your own dog since you'll have more of an interest in those topics rather than learning theoretical stuff that you may never use. It is definitely helpful to understand how to interpret blood chemistry and urinalysis - I can find some links later to post about that subject. That understanding has been particularly helpful to me and has served me well over the years, especially with geriatric dogs.
The internet is a powerful tool and has been so helpful to me - but one must be able to discern credible sources of information as there is a ton of "crap" on the internet. I always try to post links for further reading when I discuss a specific health topic here or in other dog internet groups. There are some great sites for pet owners that have more simple explanations, and there are good sites for vets that can be accessed by laypeople also.
To Anne's specific question about diabetes - if Ella had symptoms and your vet did blood chemistry and urinalysis, it should be pretty easy to diagnose diabetes. As far as learning in general - you are correct that there is "so much" and there is not really a "dummy version" that is going to be comprehensive about listing all medical conditions. But there are many sites that are helpful with learning about specific conditions, such as this one:
http://www.marvistavet.com/html/canine_diabetes_center.html
Pat