Could you book a table for this evening?
'Stasera' — stress the second syllable: 'sta-SE-ra'. It is one word meaning 'this evening'.
Ask the concierge to make a restaurant reservation on your behalf. This is a core concierge service and they will often get priority bookings.
'Prenotarmi un tavolo' = 'to book a table for me'. 'Tavolo' is the table; 'per stasera' = for tonight. Italian restaurants almost always require reservations, especially at dinner. Walk-ins are possible but risky.
Per quante persone?
For how many people?
The concierge will ask this — be ready to answer
Potrebbe prenotarmi un tavolo per due per le otto?
Could you book a table for two at eight?
Full request with party size and time
Preferisco un posto tranquillo, non troppo rumoroso.
I prefer a quiet place, not too noisy.
Adds a preference for atmosphere
Dinner in Italy typically starts later than in northern Europe or the US — 8:00 to 9:30 pm is normal. Restaurants often have two seatings. Arriving before 7:30 pm may mean eating alone among tourists; locals arrive later.