When sitting down to write anything, not just about music, this should be one of the first questions you ask yourself. The typical of reader of music journalism could be anybody based on the topic you are writing about. Knowing who would be reading your article should set the stage for how your article is written.
Take writing about the financial aspect of the music business for example. Think of who would be reading about the money aspect of it. You can probably assume that the people reading it already have some sort of background or knowledge to the inner workings of the financial aspect. This will help in picking and choosing what details you should include. If you know the people reading know all about banking and business terms, then you do not need to dumb the words down or include definitions.
The same goes for writing about artists too. If you were to write career retrospectives on One Direction and The Who, imagine who would be reading both. Your target audience will probably be drastically different. Imagine you make a YouTube video showcasing the career of One Direction. The audience will primarily be younger than if you write about The Who for a local newspaper. Language and word usage would be different.
Where you work also plays a tremendous part as well. Readers of a particular website or magazine have come to expect that articles or reviews from there are written in a very similar style. Your typical music blog will read entirely different than a music journalism piece in Variety.