Which is the correct response to the question given? ¿a quién se los das? te los doy a juan. juan me los da. se los doy a juan.

This is a good example of the usage of se in order to substitute the indirect object (also called indirect complement) le or les.  

What does this mean?  

Let’s begin by explaining that the Indirect Object of a sentence is the person, animal or thing that indirectly receives the action of the verb.  

To identify it in a sentence, we must ask to the verb ¿a quién? (to whom?) Or ¿para quién? (for whom?)  

Now, the Indirect Object Pronouns replace a word or phrase, which in the sentence fulfills the function of indirect object.  

They are written before the verb, when it is conjugated.  

These pronouns are listed below:  

1st person singular Yo: me  

2nd person singular (informal) Tú: te  

2nd person singular (formal) Usted: le  

3rd person singular Él/Ella/eso/esa: le  

1st person plural Nosotros: nos  

2nd person plural Ustedes (In latinAmerica): les  

2nd person plural Vosotros (In Spain): os

3rd person plural Ellos/Ellas: les  

For example, in the case of the question:

¿A quién se los das? (Who are you giving them to?)

Which is a question referring to giving plural items or things.

The answer is:  

Le doy (esos) a Juan (I give them to Juan)  

Being Juan who indirectly receives the action of the verb give, therefore the indirect object of the sentence. Then, knowing Juan is the 3rd person singular Él (he); the indirect object pronoun in Spanish is le.  

This is where the personal pronoun se comes in, as an Indirect Complement, and replacing le or les (indirect object pronouns), immediately followed by one of the following pronouns depending on the direct object (the part of the sentence that directly receives the action):  

lo (singular masculine)  

la (singular femenine)  

los (plural masculine)  

las (plural femenine)  

In this case los is used because them (which is the direct object) is masculine and plural, therefore the sentence:  

Le doy (esos) a Juan  

Changes to:  

Which is finally the right answer.  

show the underlined word, so i can you. or spell it