Non capisco il senso di questa frase.

Non is the standard way to make a sentence negative in Italian. It usually goes directly before the verb.

So:

• capisco = I understand
• non capisco = I do not understand / I don’t understand

This is very regular in Italian:

• Non so = I don’t know
• Non ho tempo = I don’t have time
• Non vedo niente = I don’t see anything

So in Non capisco il senso di questa frase, non simply negates capisco.

Capisco is the first person singular of the verb capire in the present tense.

So:

• capire = to understand
• capisco = I understand

Full present tense of capire:

• io capisco = I understand
• tu capisci = you understand
• lui/lei capisce = he/she understands
• noi capiamo = we understand
• voi capite = you all understand
• loro capiscono = they understand

A learner may notice that capire does not become capo or something similar for I. Instead, it becomes capisco. That is normal for many Italian -ire verbs that use -isc- in some forms, such as:

• finire → finisco
• preferire → preferisco
• capire → capisco

Yes, you can say Io non capisco il senso di questa frase, but Italian often omits subject pronouns when they are not needed.

That is because the verb form already tells you who the subject is:

• capisco already means I understand

So the most natural neutral version is:

• Non capisco il senso di questa frase.

Adding io is possible, but it usually adds emphasis, contrast, or clarity:

• Io non capisco il senso di questa frase, ma lei sì.
  I don’t understand the meaning of this sentence, but she does.

So:

• without io = normal, neutral
• with io = more emphatic or contrastive

Italian uses definite articles much more often than English does. In this sentence, il senso means the sense / the meaning.

So:

• il = the
• senso = sense, meaning

Even where English might sometimes sound natural without an article, Italian often prefers one.

Here, il senso di questa frase means something like:

• the meaning of this sentence
• the point of this sentence
• what this sentence means

Using il makes the phrase sound complete and natural in Italian.

Not always exactly. Senso can mean several related things, depending on context:

• sense
• meaning
• point

In this sentence, il senso di questa frase is very natural and usually means:

• the meaning of this sentence
• the point of this sentence

A related word is significato, which also means meaning.

Compare:

• Non capisco il senso di questa frase.
  I don’t understand the sense/point/meaning of this sentence.

• Non capisco il significato di questa frase.
  I don’t understand the meaning of this sentence.

Both are possible. Very roughly:

• significato often sounds a bit more directly like literal meaning
• senso can feel a bit broader, like sense, point, or what it’s supposed to mean

In many everyday situations, though, they overlap a lot.

Di here means of.

So:

• il senso di questa frase = the meaning of this sentence
• literally: the sense of this sentence

This is a very common Italian structure:

• il nome di Maria = Maria’s name / the name of Maria
• la fine del film = the end of the film
• il colore della macchina = the color of the car

In your sentence, di questa frase tells you what meaning we are talking about: the meaning of this sentence.

Because questa already functions as the determiner for frase.

In Italian, you normally do not use an article together with a demonstrative like questo / questa in this kind of standard structure.

So you say:

• questa frase = this sentence
• il senso di questa frase = the meaning of this sentence

Not:

• della questa frase ✘

Why? Because della already contains an article:

• della = di + la

But questa frase does not take la in front of it here. So the correct form is simply:

• di questa frase

Because frase is a feminine singular noun, and questa must agree with it.

Italian demonstratives agree in gender and number with the noun:

• questo libro = this book
• questa frase = this sentence
• questi libri = these books
• queste frasi = these sentences

So:

• frase = feminine singular
• therefore: questa frase

Even though frase ends in -e, it is feminine. Italian nouns ending in -e can be either masculine or feminine, so gender has to be learned case by case.

Yes. Non capisco questa frase is perfectly natural and often more direct.

Compare:

• Non capisco questa frase.
  I don’t understand this sentence.

• Non capisco il senso di questa frase.
  I don’t understand the meaning / sense / point of this sentence.

The second version is more specific. It suggests something like:

• I understand the words, but not what the sentence is trying to say
• the sentence seems unclear, confusing, or odd

So:

• Non capisco questa frase = broader
• Non capisco il senso di questa frase = more specifically about the meaning or point

The word order is completely normal and natural.

Standard order here is:

• Non
  • capisco
    • il senso di questa frase

Italian word order is often similar to English in simple sentences, though it is sometimes more flexible.

This sentence is the most neutral way to say it. You could change the order for emphasis, but that would sound less basic and less neutral. For example:

• Il senso di questa frase non lo capisco.

That is possible, but it is more marked and emphatic. For a learner, the original sentence is the best model.

You can absolutely use it in everyday conversation. It sounds natural and standard.

It is neither extremely formal nor especially slangy. It works well in many situations:

• in class
• while reading
• in conversation
• when asking for clarification

If you want something slightly simpler and more conversational, you could also say:

• Non capisco questa frase.
• Questa frase non ha senso per me. = This sentence doesn’t make sense to me.
• Non capisco cosa vuol dire questa frase. = I don’t understand what this sentence means.

But the original sentence is fully natural and useful.