Mercury in Aquarius tends to be highly intelligent, clever, up to date and communicative. Mercury here can spend tons of time online and be caught up on the latest memes, trends, slang, and global gossip. They have excellent memory of cultural moments and can use or store many references to various moments in pop culture.
If not, then Mercury in Aquarius at least has contact with many people, and different kinds of people. This can be characteristic, the native simply enjoys connecting with others, and it does not have to be in live conversation, it can be online interactions; or it can be because of their work, so their job includes high levels of social interface or teamwork; or because of their circumstances, for instance because they have a very outgoing spouse, parents that are involved in the community, or have children that have many friends or activities that they attend.
Mercury in Aquarius, much like in Capricorn, is not really a cuddly, warm communicator. Of course this depends on other aspects in the chart. Rather, he is a bit more distant, high level, friendly, interacting with everyone on a level playing field, interested in intellectual conversation, in detached observation about even the most sensitive topics, and in statistical analysis. They are fascinated by trends, by collective movements, by current events. So they may be rather politically involved or at least opinionated, and have some understanding in many related subjects, especially when they are in the sphere of collective human activity. So they can take interest in social welfare, economics, unions, organizational policy, organizational psychology, etc. Other times, Mercury in Aquarius creates a more nerdy individual that is into technology and the like. They might write software, or follow the crypto space, build their own hardware, be into hacking, or cybersecurity, or just enjoy vibe coding.
Aquarius Mercury can also absolutely be a musician, either as a producer using computers to make music, or as a traditional musician that plays an instrument. However, Mercury in Aquarius is more collaborative than individualistic, therefore, they're likely to be part of a band, an orchestra, or some kind of musical collective, even if they are a solo artist, they would still somehow participate in community settings.
And community management is also something they can do well. They're likely to have a busy inbox, exchange messages with many people, easily participate in online forums and leave long comments or even their own posts, but frequently reference the writing of others and add their own string of thoughts and reflections.
Mercury in Aquarius can also be a very friendly, outgoing individual that loves to bring other people together and organize various events. They might be particularly skilled in networking and getting many people on the same page.
Aquarius Mercury can also speak many languages, or take interest in different countries and cultures, or even in regions and dialects. The important point here is that they are observing systems rather than individual points. So they might research how an organization functions, or how a city distributes its resources, or how countries interact with one another, or be super fascinated by the map of a subway, or by bus routes, or in understanding how traffic works and why certain roads are consistently inefficient, or perhaps investigate zoning and gerrymandering. The common theme here is studying things at the system level, so again, Mercury in Aquarius is highly intelligent and NEEDS to solve more complex problems, which they can work on alone, but always with the help of research or contributions from other people. They are something like a mega-brain that borrows from the minds of many to create briefs or summaries that help other people get the big picture, which can be a very difficult task, but something fun for Mercury in Aquarius.
They can therefore be lawyers, engineers, business leaders, translators, social workers, technology professionals, public transportation workers, community managers, journalists, broadcasters, writers, retail workers, call center employees, school teachers and so much more… anything that puts them in touch with the greater public.
Additionally, given Mercury is an air sign here, these people can be really into flying objects, like UFOs, birds, airplanes, drones, kites, skydiving, angels, insects and butterflies, etc… and may themselves like to fly a drone, or frequently dream of flying, even like Spiderman swinging from building to building, but once again, the idea of having a birds' eye view and seeing everything from above, as though looking at an entire grid.
And this kind of "looking from above" is the perfect image for Mercury in Aquarius. They may love to have a top-down look at things. Or enjoy panning around Google Maps observing the topology, or seeing how the city looks from above, or in a very different sense, be kind of arrogant and look from above at other people as though they know more or know better, whilst other times they are very friendly but can be a bit dismissive or awkward if it comes to really deep emotional subjects.