Dans le journal means in the newspaper, which is the normal way to say that something appears inside a publication.
So French uses dans where English also often uses in.
Because parler needs de before the thing being discussed: parler de quelque chose.
So the structure is:
But de becomes d' before a vowel sound:
So parle d'un emploi literally means talks of/about a job.
Both can relate to work, but they are not always used in exactly the same way.
In a newspaper ad, emploi is very natural because it refers to a specific job opening or position.
In the most natural reading, it describes the job.
So the sentence means:
French can sometimes allow this kind of attachment to be figured out from context. Here, common sense helps: a job can be downtown, while it would be less likely for the ad itself to be downtown.
It is placed there to show that dans le journal describes the ad.
So:
If you moved dans le journal later in the sentence, the meaning could become less clear or sound awkward, because it might seem to describe emploi instead.
French word order often helps show which phrase belongs to which noun.