To dream that you are knocking at the door, means that youre trying to get into the new chapter of your life. If the doors are opened, you will get through very easily. If you hear knocking at the door, it could mean new opportunities in your waking life. Sometimes the actual knocking while you sleep makes you dream of knocking the door which means nothing.
Read more about dreaming of Knocker/Knocking in other dream meanings interpretations.