Ma fille répond que ce jouet en solde lui plaît le plus.

Because ma fille is third-person singular: my daughter / she.

The present tense of répondre goes like this:

• je réponds
• tu réponds
• il / elle répond
• nous répondons
• vous répondez
• ils / elles répondent

So with ma fille, you need répond.

Here que means that and introduces a new clause:

• Ma fille répond = My daughter answers
• que ce jouet en solde lui plaît le plus = that this toy on sale pleases her the most

So que is a conjunction, not a question word here.

English often drops that, but French usually keeps que:

• She says that...
• Elle dit que...

The same thing is happening with répond:

• She answers that...
• Elle répond que...

Because jouet is a masculine singular noun that begins with a consonant sound.

French uses:

• ce before masculine singular nouns starting with a consonant sound
  
  • ce livre
  • ce jouet
• cet before masculine singular nouns starting with a vowel sound or mute h
  
  • cet ami
  • cet hôtel
• cette for feminine singular
  
  • cette voiture

So jouet takes ce.

En solde means on sale, discounted, or marked down.

So:

• ce jouet en solde = this toy on sale

It is a common French expression. It comes after the noun, which is normal in French for many descriptive phrases.

Compare:

• un jouet en solde = a toy on sale
• des jouets en solde = toys on sale

Notice that en solde stays the same form.

In French, many descriptive elements come after the noun.

English often says:

• this discounted toy

French often prefers:

• ce jouet en solde

So instead of putting everything before the noun, French frequently uses a phrase after it.

You can think of en solde as a short descriptive expression attached to jouet.

Here lui means to her.

The verb plaire works differently from English to like.

French structure:

• ce jouet plaît à ma fille
  = this toy pleases my daughter

When à ma fille is replaced by a pronoun, it becomes lui:

• ce jouet lui plaît
  = this toy pleases her
  = she likes this toy

So lui is an indirect object pronoun.

French can use aimer, but plaire has a different structure and a slightly different feel.

• Elle aime ce jouet = She likes/loves this toy
• Ce jouet lui plaît = This toy pleases her / She likes this toy

With plaire, the thing liked becomes the grammatical subject:

• ce jouet = the thing doing the pleasing
• lui = the person who feels pleased

This is one of the most important things to notice in the sentence: French is not saying she likes the toy in the same structure as English.
It is saying the toy pleases her.

Because plaire takes à before the person:

• plaire à quelqu’un = to please someone

That means the person is an indirect object, not a direct object.

So:

• à ma fille → lui
• not la

Compare:

• Je vois ma fille → Je la vois
  because voir takes a direct object
• Ce jouet plaît à ma fille → Ce jouet lui plaît
  because plaire takes an indirect object

Le plus means the most.

So:

• ce jouet lui plaît le plus = this toy pleases her the most
• more naturally in English: she likes this toy the most

This is a superlative. It suggests there are several toys or options, and this one is her favorite among them.

Compare:

• plus = more
• le plus = the most

Examples:

• Ce jouet lui plaît plus que l’autre. = She likes this toy more than the other one.
• Ce jouet lui plaît le plus. = She likes this toy the most.

It usually means among a group of possible choices, this is the one she likes most.

So the sentence implies something like:

• among the toys
• among the sale items
• among the available options

French does not need to say the full comparison if it is clear from context.

If you wanted to be more explicit, you could say something like:

• Ce jouet est celui qui lui plaît le plus.
  = This toy is the one she likes the most.

But the original sentence is perfectly normal if the comparison set is already understood.

Because French object pronouns normally come before the conjugated verb.

So:

• Ce jouet plaît à ma fille
  becomes
• Ce jouet lui plaît

The order is:

• subject: ce jouet
• pronoun: lui
• verb: plaît

This placement is very common in French:

• Je lui parle
• Elle me voit
• Nous vous répondons

So once à ma fille becomes lui, it moves in front of the verb.

Plaît is pronounced roughly like play in English, though with a French vowel quality.

It comes from the verb plaire.

The accent mark is part of the standard spelling:

• il plaît

You may also see that the circumflex in forms like plaît is sometimes omitted in spelling reforms, but plaît is still the traditional and very common spelling.

A rough pronunciation of the whole sentence is:

• Ma fille répond que ce jouet en solde lui plaît le plus
• roughly: ma fee-yuh ray-pon kuh suh zhway ahn sold lwee play luh ploo

That is only an approximation, but it can help you get started.

Yes. Répondre can introduce reported speech with que.

Examples:

• Il répond qu’il est prêt. = He answers that he is ready.
• Elle répond que non. = She answers no.
• Ma fille répond que ce jouet en solde lui plaît le plus.

If you want to mention the person being answered, you can add à:

• Ma fille répond à sa mère que...
  = My daughter answers her mother that...

So répond que is completely normal French.