L'epilogo lascia un finale aperto.

Because Italian normally uses elision before a singular noun that begins with a vowel.

So:

• il
  • epilogo becomes l'epilogo

The apostrophe shows that the vowel in il has dropped. This is very common:

• l'amico
• l'uomo
• l'epilogo

Epilogo is masculine singular.

That can be slightly confusing because l' is used with both masculine and feminine singular nouns before vowels. So the article alone does not tell you the gender.

Useful forms:

• singular: l'epilogo
• plural: gli epiloghi

Lascia is the third-person singular present indicative of lasciare.

So it matches the subject l'epilogo:

• l'epilogo lascia
• il film lascia
• la scena lascia

In this sentence, it means something like leaves in the sense of results in / leaves us with.

Because lasciare is a transitive verb here, so it takes a direct object.

Structure:

• L'epilogo = subject
• lascia = verb
• un finale aperto = direct object

So Italian does not need a preposition like a here.

Here, finale is a noun.

It means ending or finale, and aperto describes it.

So the structure is:

• un finale = a/an ending
• aperto = open

This can confuse English speakers because finale/final looks like it might be adjectival. In Italian, finale can indeed also be an adjective in other contexts, for example:

• il capitolo finale = the final chapter

But in un finale aperto, it is clearly being used as a noun.

Because aperto agrees with finale, and here finale is a masculine singular noun.

Italian adjectives must agree in gender and number with the noun they describe.

So:

• un finale aperto = masculine singular
• dei finali aperti = masculine plural

Because in Italian, descriptive adjectives often come after the noun.

So finale aperto is the normal and natural order.

That is especially true in many common set expressions. Finale aperto is a very standard way to say open ending.

If you reversed the order, it would sound unusual or unnatural in this context.

They are related, but not the same thing.

• epilogo = the epilogue, the closing section at the end
• finale = the ending or outcome

So the sentence is distinguishing between:

• the part of the work called the epilogue and
• the kind of ending the whole work has

In other words, the epilogue leaves the story with an unresolved or open ending.

Yes. Finale aperto is a common and natural expression in Italian, especially when talking about:

• films
• novels
• TV series
• plays

It refers to an ending that is not fully resolved and leaves some questions unanswered.

So this is a very useful phrase to learn as a chunk:

• un finale aperto

A simple approximation is:

l'epilogo lascia un finale aperto
eh-PEE-lo-go LAH-sha oon fee-NAH-le ah-PEHR-to

A few pronunciation notes:

• gli does not appear here, so nothing tricky there.
• ci/cia in lascia sounds like sha
• stress falls on:
  • epìlogo
  • làscia
  • finàle
  • apèrto