Can you tell me when we arrive?
'Arriviamo' — ar-ri-VYA-mo. Stress on the third syllable; the 'ia' is a diphthong.
Ask a fellow passenger in an informal way to alert you when you reach your stop. This is useful when you are unsure and cannot read the station signs easily.
'Mi puoi dire' is the informal (tu) modal construction: 'puoi' from 'potere'. Compare the formal version: 'Mi può dire' using the Lei form. 'Quando arriviamo' is an indirect question; in Italian indirect questions do not invert the subject and verb.
Mi avvisa quando arriviamo a Duomo?
Can you let me know when we arrive at Duomo?
Formal version using 'avvisare' (to notify).
Questa è la mia fermata?
Is this my stop?
Use when the train is already slowing down.
Siamo arrivati?
Have we arrived?
Quick check when you wake from a doze.
Asking a fellow passenger to wake you or alert you is quite common in Italy, especially on long suburban rail journeys. Italians are generally willing to help — and will often start a longer conversation as a result.