Observer pattern help THANKS

[namehere44]

Am I implementing it correctly? (used for a quiz application)
Observer.h:

#ifndef OBSERVER_H
#define OBSERVER_H

#include <vector>

class Observer
{
public:
    virtual void update() = 0;
    virtual ~Observer() {}
};

class Subject
{
private:
    std::vector<Observer*> observers;

public:
    virtual ~Subject() {}

    void registerObserver(Observer* obs)
    {
        this->observers.push_back(obs);
    }

    void unregisterObserver(Observer* obs)
    {
        this->observers.erase(std::find(this->observers.begin(), this->observers.end(), obs));
    }

    void notify()
    {
        for (auto obs : this->observers)
        {
            obs->update();
        }
    }
};

#endif // OBSERVER_H 

QuizSession.h:

#ifndef QUIZSESSION_H
#define QUIZSESSION_H

#include "Observer.h"
#include "Question.h"
//#include "FileManager.h"
#include <fstream>
#include <iostream>
#include <algorithm>

using std::ifstream;
using std::ofstream;
using std::endl;
using std::vector;
using std::sort;

class QuizSession : public Subject
{
public:
    QuizSession() {
        //FileManager::loadQuestions(this->questions);

        ifstream f("/home/sysadmin/PracticPractice/questions");
        int id;
        string text;
        string answer;
        int score;
        string delimiter;

        while (f >> id && getline(f, delimiter, ';') && getline(f, text, ';') && getline(f, answer, ';') && f >> score) {
            auto question = Question(id, text, answer, score);
            questions.push_back(question);
        }

        f.close();

        sortQuestions();
    }

    ~QuizSession() {
        //FileManager::writeQuestions(this->questions);

        ofstream g("/home/sysadmin/PracticPractice/questions");
        for (const auto &q : questions) {
            g << q.getId() << ';' << q.getText() << ';' << q.getAnswer() << ';' << q.getScore() << endl;
        }

        g.close();
    }

    void addQuestion(Question &q) {
        questions.push_back(q);
        sortQuestions();
        this->notify();
    }

    vector<Question> getQuestions() { return this->questions; }

    // Descending by score
    void sortQuestions() {
        sort(questions.begin(), questions.end(), [&](const Question &q1, const Question &q2){
            return q1.getScore() >= q2.getScore();
        });
    }

private:
    vector<Question> questions;
};

#endif // QUIZSESSION_H