My sister wanted to convey the idea that she works somewhere and she used this sentence which I found quite odd. I tried looking for similar sentences but only found sentences like, 'she does odd jobs' which sounds perfectly fine. But saying 'I do a job' sounds very wrong grammatically and otherwise.
I have a job
means I am employed or I work.
I do a job
The sentence isn't ungrammatical, but the use of the verb "do" in the context is far less common. You usually say:
I have a job.
I am working or I work.
I am employed.
I am in a job (though less common).
In BrE, you can also say:
I am in work.
"I do paint houses" is a valid statement.
Usually people will say "I paint houses".
The exact sentence you said is valid English. (However, since most people do a job of some sort, the sentence seems to have little point, just like "I breathe" is usually something that people safely assume.)
In what context would you use this phrase? Variations of the phrase that would be used more often are "I did a job [where I...]" as in past tense.
If you're talking about being employed, try using "My job is..." or a longer version like "I work at (somewhere, e.g. Intel) where I (job e.g. build computers)."
I do a job. The sentence is grammatical.
Incorrec:With the right tools, I could make the job in five minutes. Correct: With the right tools, I could do the job in five minutes.
Do a job (NOT make ):
'There are lots of jobs to do when we get home.' (= pieces of work) 'There's no need to thank me. I was just doing my job.' (= what I do to earn a living)
Reference :Longman Dictionary of Common Errors.