Lesquels de ces outils veux-tu prêter à ton père demain ?

Lesquels means which ones and is an interrogative pronoun. It stands in for the noun instead of repeating it.

It has to match the noun it refers to:

• lequel = which one? (masculine singular)
• laquelle = which one? (feminine singular)
• lesquels = which ones? (masculine plural)
• lesquelles = which ones? (feminine plural)

Here it refers to outils, which is masculine plural, so lesquels is the correct form.

You can say Quels outils veux-tu prêter à ton père demain ? That is also correct.

The difference is this:

• quels is a determiner: it goes directly before a noun
  → quels outils
• lesquels is a pronoun: it replaces the noun
  → lesquels

So:

• Quels outils... ? = Which tools... ?
• Lesquels... ? = Which ones... ?

What you cannot say is lesquels outils, because lesquels does not directly go before a noun.

French uses de in this kind of selection structure: which ones of these tools.

So lesquels de ces outils means which ones among/of these tools.

Compare:

• Lesquels veux-tu prêter ? = Which ones do you want to lend?
  This works if everyone already knows what things you are talking about.
• Lesquels de ces outils veux-tu prêter ? = Which ones of these tools do you want to lend?
  This clearly identifies the group you are choosing from.

This is inversion, a standard French way to form a question.

Normal statement order:

• Tu veux prêter... = You want to lend...

Question with inversion:

• Veux-tu prêter... ? = Do you want to lend...?

English often uses do in questions, but French does not. Instead, French often changes the order of the verb and subject pronoun.

So:

• tu veux = statement order
• veux-tu = question order

In French inversion, the verb and the subject pronoun are linked with a hyphen.

So you write:

• veux-tu
• aime-t-il
• peut-elle

The hyphen is required in this structure.

French sometimes inserts a -t- in inversion for pronunciation, but only in certain cases, usually when the verb ends in a vowel sound and the pronoun starts with a vowel.

For example:

• a-t-il
• va-t-on

Here, veux already ends in a consonant sound, so no extra t is needed:

• veux-tu, not veux-t-tu

Because prêter works like this:

prêter quelque chose à quelqu’un
= to lend something to someone

So in this sentence:

• lesquels de ces outils = the thing being lent
• à ton père = the person receiving them

That is why à is used.

This is a very common point for English speakers.

• prêter = to lend
• emprunter = to borrow

They describe the same situation from opposite sides.

Examples:

• Tu prêtes un outil à ton père.
  = You lend a tool to your father.
• Ton père emprunte un outil.
  = Your father borrows a tool.

So in your sentence, the subject is the person giving the tools, which is why prêter is used.

Because père is a masculine singular noun, so the correct possessive adjective is ton.

French possessive adjectives agree with the thing possessed, not with the owner.

So:

• ton père = your father
• ta mère = your mother
• tes parents = your parents

Because au père would mean to the father, not to your father.

Here the sentence specifically says your father, so French uses the possessive:

• à ton père = to your father

Also, contraction happens with:

• à + le = au
• à + les = aux

But there is no contraction with ton, so:

• à ton père stays à ton père

No, but the end is a very natural place for it.

In the original sentence, demain comes last because that is a normal, neutral position for a time adverb.

You could also say:

• Demain, lesquels de ces outils veux-tu prêter à ton père ?

That puts more emphasis on tomorrow.

So the original order is not the only possible one, but it is very natural.

It is standard and perfectly correct. Because it uses inversion, it sounds a bit more careful or written than very casual everyday speech.

A native speaker might also say:

• Tu veux prêter lesquels de ces outils à ton père demain ?
• Lesquels de ces outils est-ce que tu veux prêter à ton père demain ?

All three are correct, but they have slightly different levels of formality:

• inversion = more formal/standard
• est-ce que = neutral
• intonation only = more casual

A rough English-friendly pronunciation is lay-KELL.

A few useful notes:

• the final s is silent
• the qu sounds like k
• the stress is not as strong as in English

In the whole phrase ces outils, there is a liaison:

• ces outils sounds roughly like say-zoo-tee

So part of the sentence sounds approximately like:

• lay-KELL duh say-zoo-tee

This is only an approximation, but it is a helpful starting point.