I want to know how / if we could train monkeys to do a variety of human tasks. Is it possible to teach monkeys human trades and set them free throughout major cities to do jobs and interact with humans?
Not without majorly altering the monkeys to the point where they aren't monkeys anymore and its a new subspecies. They aren't smart enough. The expression 'Monkey see, monkey do' comes to mind - they can be trained, yes. They can be trained to do things. But there's no way for them to go 'Planet of the Apes' on us. Thankfully.
japan do that and most south east asian country also train monkey for certain activity, from picking coconut or other fruit to street circuss to act like human like riding bicycle,smoking, even as drug cartel, etc.
i dont know about japan but the training that i know though..... is pretty much would make animal lovers like PETA mad because it choke the monkey with chain to force them standing in two feet etc and pretty much torture them, picking coconut and drug cartel is more humane though because you give a treat as their payment (yes they understand some kind of value) and not require them to standing in two feet.
also if you want the monkey into military they probably do better as grenade thrower because they naturally know how to do it.
and i just want to put this image just because
You can train apes to do human jobs, but I doubt it would be worth the trouble.
Apes can understand the concept of work and payment, but their ability to grasp complex tasks is, on average, much lower than that of humans. They can also be moody, prone to distraction, and have their own personality traits that differ significantly from those of typical humans. Chimpanzees, for instance, are very aggressive and nearly impossible to control.
Instead of thinking of them as trained animals, think of them as severely mentally handicapped humans with serious personality disorders. They can be put to work, but in many cases this will prove a liability.
You can do whatever you want in the fictional world but you need to understand that they will not be monkeys in the way we know them in this reality. They have no sense of value in anything beyond basic family or troop relationships, so “money” means nothing to them. Damaging property, stealing, giving things away, will never be concepts true monkeys can understand. They won’t arrive to work on time because they don’t know what time means. They will do whatever makes them feel good.
In your alternate world, you will have to give your monkeys a higher IQ and an ability to understand abstract thoughts, and to reciprocate moral values. The basic concept of a “troop” exists with real monkeys, and that could be developed in your story into an understanding of citizenship and civic duty after their intelligence is improved.
Again you can’t pretend these are “real monkeys” as we know them in this reality. If being “real monkeys” is crucial to your story, then the answer is simply, no.
genetically engineer (uplift), then teach, yes.
but uplifting a species is still way beyond our ability you would need severely advanced genetic engineering, likely generations away. Our first uplift will also be a more intelligent species likely an ape (although we could drive the rest of apes extinct before we get there), lastly our first uplift will also be largely trail and error, so they will spend a long time, generations, in the testing phase.
We are still at the stage that we don't know most of the molecular mechanism that how our body works. Even one day we know that, we still don't know how brain-to-mind works. So we can never be sure whether we can train monkey (or any specie that have a complex enough brain) to do advanced human things. Without theory support, the only thing we can do is to try and try like Edison did.
For complex and mysterious system like brain/mind, every thing is possible, it just still doesn't happen. Maybe a new special method of stimulation/training, or maybe a few gene modifications that make monkey trainable with existing methods. Any of this will triger another revolution like the 20th century physics did.
But the key is that that is not enough. You train moneys to be like human, then they will demand rights and more, and finally get that through wars just like we did. They won't work without demand like you expected. They are just us, and there are already enough us and we don't need more. So the even more hard question is how to train money to be human with no demands which I suppose is impposible.