Hubs have enough standard features that anyone generally familiar with hubs can usually determine how to service them.
Cartridge bearings come in standard sizes, and these are generally printed on the rubber seals. Once you expose the bearings, you should only need to look closely at the seal to find a numeric code, e.g. 6802. Each code corresponds to a set of measurements - external diameter, internal diameter, and depth. (Admittedly, proprietary cartridge bearings do exist, but these should be rare, and manufacturers using them are going to provide the service manuals.)
To get the end caps off, you usually can use a pair of Allen wrenches. Hold one endcap with one wrench, and unscrew with the other. Some endcaps are friction fit, i.e. you simply pull them off.
Freehub bodies are often held on by screwed-on endcaps. Some freehub bodies are pulled off without unscrewing the endcap - remember that your thru axle or quick release holds the system together, so there's no risk of the freehub body coming off while riding.
You do need bearing extractors and presses to remove the bearings from the hub or the freehub body and to refit new bearings. If you want to do your own work, you can find general purpose extractors and presses that fit a variety of parts. Bike stores will also have these items.
As Adam stated in a comment, many hubs with anonymous branding are made by third party companies like Novatec, Bitex, and others. These OEM manufacturers tend to be based in Taiwan. DT Swiss often supplies hub internals on an OEM basis to other manufacturers, and it makes its own branded line of hubs. Even if you can't determine who made the hub, you can still service it. If you need to replace the freehub body wholesale, it's best to contact a Specialized dealer or distributor. They should be able to look up the part in their system. Riders who come across an old OEM wheelset where the manufacturer can't locate spares may be out of luck if they need to replace a freehub body, a bent axle, endcaps, or parts other than the bearings.
As I alluded to above, some hubs have proprietary parts. Generally, these are rare. For example, I had a pair of Alchemy hubs. These were lightweight, high-performance hubs. Wheels Manufacturing later bought the designs to Alchemy, and supported existing hubs that they had parts for, but they later discontinued the hub. While they did this, they did send out a replacement front axle, as I had somehow managed to bend the lightweight axle while doing general road rides at 135-140 lbs. Later on, when I needed the bearings changed in the rear hub, the shop discovered that one of the bearings needed a proprietary tool to remove, which was no longer available as Alchemy itself had gone out of business and Wheels didn't provide that tool. I digress, as I often do, but we can derive a lesson from this: most cyclists should avoid proprietary parts. If you feel you must go this route, you might want to consider an established manufacturer with a long presence, e.g. I'd happily consider Campagnolo's factory wheels if I ever went back to using Campagnolo. With cheaper OEM wheels, the proprietary parts issue should only strike you if you need to replace something other than a bearing, and the hub is unlikely to need proprietary tools to service anyway. In any case, you may be ready to upgrade by then.
