Upvote:2
There are trains from Treviso Centrale to Trieste. Check on bahn.de. You most probably wont make the last train from Sezana, so spend the night in Trieste.
Upvote:3
As is often the case for European rail route related queries, the Man in Seat 61 has you covered!
The brief summary (see the seat61 page for full details) is: