Dopo la visita, la diagnosi è semplice.

In Italian, singular countable nouns usually need an article. So visita normally becomes la visita when you mean the visit.

• dopo la visita = after the visit
• dopo visita would sound incomplete or unnatural in standard Italian

This is a common difference from English, where articles are sometimes omitted more easily.

Dopo means after here. In this sentence, it functions as a preposition, followed by a noun phrase:

• dopo la visita = after the visit

It can also be used as an adverb in other contexts:

• Prima mangio, dopo studio. = First I eat, then I study.

So dopo can mean either after or later/then, depending on the structure.

The comma separates the introductory time phrase from the main clause:

• Dopo la visita, = after the visit
• la diagnosi è semplice. = the diagnosis is simple

In Italian, this comma is natural and helps readability, especially when a phrase comes at the beginning. It is not absolutely required in every short sentence, but it is very common and perfectly correct here.

Yes, diagnosi is feminine singular: la diagnosi.

This can be confusing because many learners expect words ending in -i to be plural. But diagnosi is one of several nouns of Greek origin that end in -si and are feminine singular in Italian.

Examples:

• la diagnosi
• la crisi
• la tesi
• l’analisi

So in this sentence:

• la diagnosi = the diagnosis

The plural is also diagnosi.

So:

• la diagnosi = the diagnosis
• le diagnosi = the diagnoses

The article changes, but the noun itself does not.

È is the third-person singular of essere: is.

The accent is important because it distinguishes è from e:

• è = is
• e = and

So:

• la diagnosi è semplice = the diagnosis is simple
• la diagnosi e semplice would be incorrect

In writing, the accent should always be included.

Semplice is an adjective, and here it agrees with la diagnosi, which is feminine singular. The reason it looks unchanged is that semplice has the same form for masculine and feminine singular.

Its forms are:

• semplice = masculine singular
• semplice = feminine singular
• semplici = masculine/feminine plural

Examples:

• un problema semplice
• una diagnosi semplice
• problemi semplici
• diagnosi semplici

Yes, that is grammatically possible, but it changes the rhythm and emphasis.

• Dopo la visita, la diagnosi è semplice.
  This emphasizes the time condition first: after the visit.

• La diagnosi è semplice dopo la visita.
  This starts with the diagnosis and adds the time information afterward.

Both are correct, but the original sentence sounds more natural if the speaker wants to frame everything in terms of when the diagnosis becomes simple.

Normally, no. In Italian, a singular noun used as the subject of a sentence usually needs an article.

So:

• la diagnosi è semplice = correct
• diagnosi è semplice = generally incorrect in standard Italian

Italian uses articles more often than English does. This is something learners notice very quickly.

Very likely, yes. Visita can mean visit in general, but in medical contexts it often means:

• a medical examination
• a doctor’s appointment
• a consultation

Since the sentence also contains diagnosi, the most natural interpretation is medical:

• Dopo la visita, la diagnosi è semplice.
  = After the examination/appointment, the diagnosis is simple.

Usually yes, but the nuance can vary with context. In a sentence like this, semplice could mean:

• easy to make
• straightforward
• clear
• not complicated

So la diagnosi è semplice might suggest:

• the diagnosis is easy to determine
• the diagnosis is straightforward once the visit has taken place

Italian semplice often overlaps with both simple and straightforward in English.