Htydjtk

Goblins are small, diminutive humanoid creatures. They are approximately the size of a small child, they are short-lived, and they have very low intelligence.

In my fantasy world, goblins have been bred and domesticated like dogs. They can be taught simple commands and tasks, though they lack the intelligence for any skilled labor. They can use tools, but they still require oversight. Their lifetimes are too short to be worth much investment.

They are basically dogs with opposable thumbs.

Goblins have been bred to work on castles, farms and stables, etc. doing all the menial jobs. They are best suited for repetitive tasks that require no thought.

They are not paid, and will work because that's what they've been bred to do.

Like dogs, some goblins are prone to distractions and will occasionally be mischievous. They cannot be trusted with anything valuable.

They have very little strength, but decent stamina. Goblins can also eat near anything, and are very easy to sustain - they will happily live off trash and leftovers. They have good sense of smell, and are decent hunters. They work well in numbers.

Domesticated or no, most animals will spook around goblins. Also, the sight of fire can send a goblin into a craze.

There is a risk of goblins going wild if left unsupervised.

Right now, I'm thinking that goblins will be used to wipe the floors and clean stables. Are there any other jobs in medieval-like setting where domesticated goblins could be employed?

Agriculture: Goblins can do anything larger animals can't do. It shouldn't be too difficult to teach them to harvest crops, vegetables and fruit, take care of the plants in general, get rid of unwanted weeds, sow seeds etc.
They might even lead larger animals for plowing.

Manufacturing can also be made easier. If they can clean, anything for textiles for example
- shearing sheep, spinning, weaving and so on - shouldn't be hard, and a lot more I'd assume. Later on they'd be ideal factory workers.

While their lacking strength can be a drawback, their stamina and size can also be useful in mining. Again, a support position is where they'd be best - move small rubble out of the way, collect and sort ore while the human miner works the pickaxe.

In general if goblins existed the way you describe them they'd be useful for almost anything at least in a support job. While they couldn't work as blacksmith themselves, for example, it wouldn't be a problem for them to operate the bellows, add coal to the furnace, clean and order tools and so on.

Other than typical work:

They can be employed as entertainment - circus, gladiator/pit fights, theater, possibly even music.

And, of course, they can be warriors. Give them spears, clubs and slings. They are faithful like a dog, but can handle weapons. Hell, they can even ride dogs for all I care... kinda depends on how uneasy domesticated animals get around them, but I'd consider it illogical to make dogs afraid of them if they live in the same household.

In other words, they'd be a part of every aspect of life and work. Nobody says no to a cheap and efficient worker.

War goblins obviously, send them in just before the first regular rank with knives and cheap spears in the hope of getting them to disprganize the enemy line just before the charge