How to find an object in an ArrayList

Suppose your class structure Librois

public class Libro {
    private int isbn;
    private String titulo;

    public Libro(int isbn, String titulo) {
        this.isbn = isbn;
        this.titulo = titulo;
    }

    public int getIsbn() {
        return isbn;
    }

    public String getTitulo() {
        return titulo;
    }
}

We create a class ProbarLibroto create the books and perform the search for a book.

public class ProbarLibro {
    //Creamos un ArrayList de libros
    static ArrayList<Libro>libros= new ArrayList<>();
    public static void main(String[] args) {        
        //creamos 2 libros
        Libro libro1=new Libro(1, "Titulo 1");
        Libro libro2=new Libro(2, "Titulo 2");
        //Agregamos los libros al ArrayList de libros
        libros.add(libro1);
        libros.add(libro2);
        
        //Buscamos un libro con isbn=2
        Libro libroencontrado= encontrarLibro(2);
        
        //Mostramos la búsqueda del libro
        if(libroencontrado!=null){
            System.out.println("Datos del libro encontrado:");
            System.out.println("ISBN: "+libroencontrado.getIsbn());
            System.out.println("Titulo: "+libroencontrado.getTitulo());
        }else
            System.out.println("No se ha encontrado ningún libro");
           
    }
    
//método para la búsqueda de un libro, esto es lo que preguntas

    public static Libro encontrarLibro(int isbnrecibido){
        Libro libroRespuesta = null;
        for (int i = 0; i < libros.size(); i++) {               
            if(isbnrecibido == libros.get(i).getIsbn()) {
                libroRespuesta= libros.get(i);                   
            }                        
        }        
        return libroRespuesta;
    
    }
}

What you are doing is almost correct, generally we search for an object based on the value of some property in this case based on the ISBN.

But remember that if this value is of type String, the comparison must be done using the .equals(..)or function .equalsIgnoreCase(..)that compares the text string against an object ignoring case. :

 for (int i = 0; i < coleccion1.size(); i++) {
     //if(isbnrecibido == coleccion1(i).getisbn()) {
     if(isbnrecibido.equalsIgnoreCase(coleccion1(i).getisbn())) { //*revisa si son iguales!
       librorespuesta = coleccion1.get(i);
       System.out.println(coleccion1.get(i));
     }
  }

One way you could make it easier to find your books is through Streams.

As a recommendation, I will tell you that there are books with ISBN 13, so a type data intwould be insufficient, so I recommend changing the ISBN to String or long.

Let's imagine that your book class is as follows:

public class Book {
    private final Long ISBN;
    private final String title;

    public Book(long ISBN, String title) {
        this.ISBN = ISBN;
        this.title = title;
    }

    public Long getISBN() {
        return ISBN;
    }

    @Override
    public String toString() {
        return String.valueOf(ISBN).concat(" : ").concat(title);
    }
}

We could find the book by its ISBN with Stream.filter and since the ISBN is unique we can limit it to the first result with Stream.limit

import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        ArrayList<Book> books = new ArrayList<>(List.of(
                new Book(9788440719171L, "El archipiélago en llamas"),
                new Book(9788475743233L, "De la tierra a la luna"),
                new Book(9788484470076L, "Escuela de Robinsones")
        ));
        Long ISBN = 9788440719171L;
        Book search = books.stream()
                .filter(book -> book.getISBN().equals(ISBN))
                .limit(1)
                .findFirst().orElse(null);

        System.out.println(search);
    }

}

Output

9788440719171 : El archipiélago en llamas

I did not understand your question very well but I think the solution to your problem is something like this

public Libro getBook(Lista<Libro> libro, int id){
    Libro<T> aux = this.front; //Siendo este el 1 libro de la lista
    Libro respuestaLibro = new Libro();
    int i = 0;
    while(i<libro.size()){
        if(aux != null)
            if(id.equals(aux.id)){
                respuestaLibro = aux;   
            }
            i++;
            aux = aux.next;
    }
    
    return respuestaLibro;
}

As I told you in the comment, be careful with ==, it is used to compare addresses and primitive types. The code I told you is an example of what I think happens to you.