May I sit here?
'Sedermi' — 'se-DER-mi'. The 'r' is softly trilled.
Use at a bus stop with bench seating when you want to sit next to someone already seated.
'Posso sedermi' combines the modal 'posso' (I can/may) with the reflexive infinitive 'sedermi' (to seat myself). This is the reflexive form of 'sedere'. A very polite and common phrase.
È libero questo posto?
Is this seat free?
Shorter alternative; 'libero' means free/available.
C'è qualcuno qui?
Is there someone here?
Indirect way of asking if the seat is taken.
Questo posto è occupato?
Is this seat taken?
'Occupato' means occupied; direct and clear.
Bus stop benches in Italy are often in short supply. In small towns, waiting passengers may stand in small groups chatting — joining the conversation is considered perfectly friendly behaviour.