How to create a peephole in a door without a hole?
If when you say the door is without a hole, but you are allowed to drill one then it is a question of deciding the height and a suitable diameter.
If you cannot drill a hole then some sort of miniature camera will be needed...
When drilling a hole through the door, making sure you go through square is crucial and a tiny pilot hole then drilling from both sides gets a clean hole - at least in my experience.
Here is one possibility: Peephole on Amazon