Hi are you working for this apartment? I am a new tenant living at 2009. Can I request a buzzer code?
Hi --> Excuse me
This one might depend on the country. I can imagine that in the USA a
Hi in this context might be more commonplace. (But then again, the way the customer-employee dynamic works there is pretty special, and not entirely like elsewhere in the world.)
Myself coming from Europe, I would suggest that if you don't yet know the local mood and atmosphere, it's safer to bet on the more polite "Excuse me": it does not risk coming in the way of building out mutual respect between you. Later on you can switch to "Hi", when you already know each other and you deem the situation suitable for it.
are you working --> do you work
"are you working here" means: "are you working right now, at this minute?"
"do you work here" means: "do you work here normally, day in day out?" which then can be logically substituted by "is this your workplace?" (which then, from the context, implies efficiently: "are you in authority regarding my request?")
I am a new tenant living at 2009 --> I have just moved in to 2009
Here, there is a difference between whether it's written in an e-mail or used in verbal speech:
Let's make a quick detour to your secondary question: how should the apartment number
2009 be pronounced? I would personally go for "two-oh-oh-nine".
Now in speech, the first variant you suggested is pretty good, however I would still substitute
in; resulting in:
I am a new tenant living in two-oh-oh-nine.
Let's see the problem in writing: "living in 2009" might imply the year
2009, which would be, at the least, confusing.
With the above suggested present perfect variant this can be somewhat avoided. So in writing this could be as precise as:
I have just moved in to apartment 2009.
Can I request a buzzer code? --> I would like to request a buzzer code.
Strictly speaking the first variant is a yes/no question — and thanks to cultural peculiarities (memes on the internet), I believe some people might be inclined to switch into this thought mode when hearing a
Can I .... The (obviously unsatisfactory, but semantically correct) answer of "Yes you can. [...and then awkward silence...]" might actually not happen; but the risk is there. :)
There is the guidance "Ask and you shall be given" from the Bible. Believe or not, I reckon with this in my speech. Therefore, I would go for the polite statement of my request.
All of it together:
Excuse me, do you work here? I have just moved in to two-oh-oh-nine; I would like to request a buzzer code.