Staying Up To Date
Bad news; you've been sued. You go to a lawyer and they're wonderful; they've spent years studying law, they've been taking cases like yours for nearly 3 decades, and they have answers to all your questions. Only one thing seems odd: a few of the regulations they've mentioned you're pretty sure don't exist anymore? You ask them about this and they say "oh, I don't keep up with changes to the laws. I just give advice according to how things worked when I passed the bar exam". You look at the law degree on their wall. It says 1996. You go find another lawyer.
This, luckily, is a pretty ridiculous story. No self-respecting professional would not take the time to update their information as things change. Ensuring that the advice they're certified to provide remains correct is the bare minimum expectation of such a role.
Anyway, let's talk about Magic Judges. As dedicated professionals who deeply care about helping each other learn and grow, no experienced, respected, L2+ judge would ever do something like run a presentation that teaches people tournament policy that's 4 years out of date, or go to a Regional Championship without having read about how the new set's mechanics work. How do we maintain such a stellar track record?
It turns out, keeping up with Magic rules and policy is actually kind of hard! The rules are long and complicated, and they have a tendency to change every 3 months. This doesn't give us a lot of time to get acquainted with them before yet another change has occurred.
Luckily, the changes tend to apply to a specific section. It's rare for the same part of a document to undergo multiple consecutive changes or for there to be one update that changes a bunch of things all over the place. This means we can safely get used to the way each part of policy is in isolation, and we need only update individual pieces of knowledge as appropriate, with plenty of time in between to get used to the new way it works.
What are the tools we can use to do this?
1. Your brain
When it comes to not being misled by old rules, knowing is half the battle. Simply being aware that any resource you're looking at may be out of date if it was released more them a few months ago is the most important step. There's a wealth of information available from the past 30 years of judging, and while much of it is still highly applicable, some of it is not. If you're reading an article or watching a video and something seems odd to you, check what date it was released on, and confirm that information with another judge or by checking the official documents.
2. The official documents
What better resource for staying up to date with the official documents than the documents themselves? The most recent version of the Comprehensive rules can always be found here or here. The most recent version of the tournament policy documents can be found here, here, or here.
3. The official update articles
Every time the CR changes, Wizards puts out an update bulletin that explains what was changed and why.
Similarly, whenever tournament policy changes, Wizards usually puts out an article explaining the changes to policy. They can't decided on where those go either, but you'll probably be able to find it on either Toby Elliott's blog, somewhere in the black hole that is the Wizards article ecosystem (using the Internet Archive as necessary), or if all else fails, by asking every judge you know for its location until one of them sends you a URL and tells you not to ask them where they got it.
Notably, neither of these articles is the release notes! The release notes are separate articles aimed towards players that provide a long list of new cards and a long FAQ about potential questions. It generally doesn't go into the rules themselves, and nearly all of the questions it covers are also covered by the much shorter rules update bulletin. There's certainly no harm in a judge reading the release notes, but they're not a replacement for the update bulletin, and as you get more familiar with reading the rules themselves, you'll find that the release notes are a waste of time and don't teach you anything you didn't already learn from the update bulletin.
4. Academy Ruins
Academy Ruins is a volunteer-maintained website designed for exactly this. It provides a diff of each new version of the rules that you can refer to to find out precisely what changed. It also has a list of all past versions of the rules and policy documents, in case you're worried you might be going crazy and want to confirm that yes, it actually did used to work that way.
5. Practice questions
While individual card examples are not a good way to learn new rules, they are a good way test your learning to make sure you learned it correctly, and to reinforce that learning such that you'll remember it in the future. There are a few ways to do this.
Firstly, there are the Judge Academy update quizzes. Every set set, JAC releases a quiz about new cards and mechanics that you can take for free. Unfortunately, these are only available to people who are paying for a certification, so they're not an ideal resource. They're also quite short and won't necessarily have as many questions as you want to practice on.
RulesGuru is a volunteer-run database of rules questions, and you can use the sidebar to filter them down to only questions about the newest set. Unfortunately, they don't currently have enough volunteers to maintain a decent-size question pool, so it's pretty light on questions about newer cards.
So for now the best option is usually going to be to get live questions directly from players. You can find these on the Ask The Judge Facebook group or the MTG Judge IRC chatroom. Players go to these places to ask about things they want to know, and anyone is welcome to provide an answer. These are very useful resources, as they give you an idea of what real players are actually asking in real life situations, not just theoretical questions that a judge wrote because they thought they were neat.
6. Case studies
Tournament reports exist! Judges who go to tournaments sometimes write up their experiences at that tournament as educational material for other judges, and in order to get feedback on their decisions. Just like live player questions, these are a wonderful window into what's actually happening at events nowadays. And any new rules or policy changes that had a noticeable impact tend to get highlighted in these reports, making them an ideal way to learn in advance what you need to be ready for. You can subscribe to email notifications of any new tournament report on the Judge Academy tournament reports forum.