Вы делаете ошибку, когда вводите данные в новое намерение. Вам нужно заменить
DatabaseReference putData = FirebaseDatabase.getInstance().getReference("ProgressReports/" + uid + "/" + id.get(i));
Intent intent = new Intent(list_view.this, ProgressReports.class);
String title = String.valueOf(putData.child("title"));
String content = String.valueOf(putData.child("content"));
intent().putExtra("titleTest", String.valueOf(title));
intent().putExtra("contentTest", String.valueOf(content));
startActivity(intent);
на
DatabaseReference putData = FirebaseDatabase.getInstance().getReference("ProgressReports/" + uid + "/" + id.get(i));
Intent intent = new Intent(list_view.this, ProgressReports.class);
String title = putData.child("title").getValue(String.class);
String content = putData.child("content").getValue(String.class);
intent.putExtra("titleTest", title);
intent.putExtra("contentTest", content);
startActivity(intent);