First of all, I'm going to assume the following about your giants' intelligence:
- They are literate, but lack the ability to use correct grammar and have a limited vocabulary.
- They cannot perform maths to a level above basic addition and times tables.
- Due to this they may be socially awkward with humans, or looked down upon for their apparent stupidity.
So, what jobs can we give them?
Let's go through some different areas:
Writing, journalism, and presenting on TV are out of the question, however roles as actors would be available to them but only for specific roles as giants.
Stacking shelves and working the checkout are viable options, since they require only simple interactions with people. We assume that shops have aisles and checkouts big enough for the giants to fit in, of course.
Serving at the counter in fast food restaurants would also be an option, however I doubt a giant would be a very good waiter, since that involves words and discussions about the food and drinks menus.
While health work is out of the question, giants may be useful for the fire services, or for riot control in the police department (especially if the rioters are other giants).
I don't think we'll be seeing any giant pilots, however some modes of transport are very simple to operate. A tram perhaps? If your giants can drive, they could serve as bus drivers and lorry drivers too.
Construction and similar industries
Probably the most obvious option. Giants could be handy in lifting stuff or operating machinery. Mining would be another big one for the giants, with their strength being handy for this kind of work.
Arts and textiles
Perhaps some of your giants are good painters, sculptors, or creators? Maybe some giants have skill in textiles or sewing? The clothes industry often includes repetitive tasks which can be learnt.
Food production and farming
While being a fully qualified chef might not be the most likely option, consider factories that mass produce foods. Some of these use workers since machinery cannot perform the tasks they want. The giants could make sandwiches, pack salads, pick fruits (no need for a cherry picker!), harvest grains, and do all sorts of jobs on the farm. Looking after sheep, cows, chickens, and other livestock does not necessarily require a degree.
While mixing giants with humans may lead to catastrophe, there could realistically be leagues in giant-sports. Their strength would be something amazing for people to witness and things like wrestling, boxing, and martial arts could be popular among giants. Also consider team sports and athletics. There may even be a Giant Olympics (or equivalent) and various world leagues available for professional sportsgiants.
Stupid giants could easily work at recycling centres, or as bin collectors. Cleaning the streets and public areas would be a simple job for them.
No! I hear you say! A stupid giant could never be a teacher! But who is going to teach the giants? Would giant children go to the same schools as human children, or to giant schools? Would those schools have human or giant teachers? Perhaps the more intelligent (or less stupid) giants could aspire to teach the next generation.
So there you have it. There's a lot of jobs out there...
Are these jobs well-paid?
Realistically, these giants would not make as much money as a more intelligent human. Due to them eating more, they would need to spend more on food. This is a bad combination. They are also very tall, making housing much larger for them and more expensive. They would also need bigger clothes, costing more money.
To be honest, I think that your giants would struggle to get by.