Substitute the values you want into the select
part of the query:
INSERT INTO questions (question_parent_id, question_subject_id, question_topic_id, question_directions, question_text, question_file, question_description, question_difficulty_type, question_has_sub_ques, question_picked_individually, question_manual, question_site_id, question_created_staff_id, question_added_date, question_appeared_count, question_updated_staff_id, question_updated_date)
SELECT question_parent_id, 8, 547,
question_directions, question_text, question_file,
question_description, question_difficulty_type, question_has_sub_ques,
question_picked_individually, question_manual, question_site_id,
question_created_staff_id, question_added_date, question_appeared_count,
question_updated_staff_id, question_updated_date
FROM questions
WHERE question_subject_id = '8' AND question_topic_id = '545';
Or, the select
might begin:
select question_parent_id, $_POST['to_subject_id'], $_POST['to_topic_id']