Your typical adult has few “formal” means to learn to read and write, and you named most of them, but there could be contacts in his city section, town, village, etc. that might be able to help learn in a more informal manner.

Quick disclaimer though, I’ll be basing this answer on information found in A Social and Cultural History of Early Modern France by William Beik, which obviously means the answer will primarily apply to France, but won’t be too dissimilar from other areas of western and Central Europe. And the answer will primarily deal with the 14th century onward. While the title focused on the early modern, it really begins the discussion in the 14th century. The book tracks trends up through the 18th century, but I’ll stick to information that would’ve applied specifically to the late medieval as well.

First, I’ll add that there’s a chance, as a commoner, especially if you’re a man, you may have learned to read and write as a child and young adult. Starting in the late medieval period, many towns, villages, city sections, started establishing local primary and secondary schools for the communities. These would’ve had virtually no official regulation, so quality of instruction could vary dramatically, and they were typically thrown together by town councils run by prominent members of the community, with the classrooms likely just being a certain room in the local church. The teachers were typically lower clergy, and usually were native to their communities and had a strong communal connection, however some were hired from elsewhere and not all teachers came from the clergy. Most of these teachers would know how to read and write, especially in the cities, but it wasn’t uncommon for poorer peasant communities in the rural countryside to make whatever they had work, and sometimes that meant even their “teacher” was uneducated and couldn’t read or write. Schools were seen as prestigious, so as time went on most communities tried very hard to open their own schools, and often these schools would be funded by basically local fundraising. There wasn’t really any national budget for schooling. Occasionally you might have a lord here or there mandate that their community open a school, but very rarely would this be funded by the lord, and the community would generally have to figure out fundraising on their own.

In your post you mentioned the example of a blacksmith. Depending on rank and guild affiliation, and especially in the cities, a man may already know how to read and write through their guild training. Or even a woman. After all there were many guilds open to both men and women. Some artisan guilds even allowed women in high ranks and leadership roles, and indeed there were also guilds that pulled the reverse, and men were not allowed, only women. Guild literacy would’ve been far more common in cities where cities often had special legal privileges for certain guilds, local regulations existed, taxes, tariffs, etc. Guilds would’ve needed to stay up to date on this information and as such there’s a decent chance higher ranked artisans would know how to read or write.

If you’re an adult and didn’t learn through either of the above methods, there might be other ways or people you know who might be able to teach you.

Of course, you could go to a college to learn, but you mentioned not being interested in scholarly or clergy methods of learning, and I assume this will also apply to fields like law or medicine, which would also require the ability to read or write and students would learn that in colleges. While these were not cheap, commoners could make it work and many did go to college. In fact college, through the legal profession, was the most common way for peasants to enter the nobility, since many legal clerk, notary, or other positions were reserved for nobles, and if you were qualified and landed a job, it was possible to be granted nobility, which was actually much more open than a lot of people would probably expect. College was expensive, but for a city section, a small village, or even a family, it was extremely prestigious for the community, and it wasn’t uncommon for a village community to pool together money so they could send their brightest young adults to college in the cities for a shot at a better life and maybe even nobility, whether it was to send them to college for law, or clergy, both had paths to noble ranks for commoners. And maybe after they graduate, this hot new, young lawyer, physician, or priest could come back to the village and fill one of these important jobs for the community they grew up in.

This is where I would say is the “best bet” for learning to read and write if none of the above options apply. No matter how poor your little community is, whether it’s a single dense street in Paris, or a tiny village in Brittany, there are likely members of your community who can read and write, and you’d just need to know who they are, and ask them nicely to teach you. Your local priest probably grew up with you in most communities. You could get with your childhood friend and ask him. Your community probably has some kind of legal clerk to assist with your local lord’s court, and same thing. There’s a very high chance that this clerk grew up in your community and was one of those “bright kids” that the community fundraised to go to college. If not a legal clerk, your community may have a notary, tax collector, or accountant, which in this period all came from basically the same college education in law, and most of these people would be able to read and write. If you’re an artisan, it’s almost guaranteed that someone in your guild can read and write, so they could teach you as well.

But that about sums up the most common commoners that know how to read and write so you could find them to learn. There are other possibilities, but they would’ve been less common, such as being taught by your lord, which some lords were super strong pillars of their communities and hired locals for odd jobs on their estates, but while an option, it probably wouldn’t be likely.

There would often also be quite wealthy peasants in the community, entrepreneurial families that have slowly gobbled up farmland over generations. In some cases, these wealthy peasants could make almost as much as, and in some cases more money, than their lords. These peasants are likely following my favorite method of attaining nobility, and that would’ve been what I like to call the “fake it til you make it” method, a long con. As such, these wealthy peasants would have a much higher chance of literacy seeing they would want to appear noble and educated in any way they could, but unfortunately that would also mean distancing themselves from other peasants so they probably wouldn’t be too much help most of the time.

I hope this helps, and I hope it fits the standards for this sub.