1, 2, and 3 mean the same thing. #1 is simpler and better stated.
4 and 5 mean the same thing. #6 could mean something slightly different. It could mean WHEN YOU ARE IN the shop at the same time the boy is. 4 and 5 mean that you could be looking into the shop from outside the shop or looking at a picture of the shop; looking at the shop without being inside the shop.
1. He is looking for the key in the room.
2. He is looking for the key which is in the room.
3. In the room, he is looking for the key.
[Does #1 mean #2 or #3? Are both okay? It is ambiguous, isn't it?]
4. Look at the boy in the shop.
5. Look at the boy who is in the shop.
6. In the shop, look at the boy.
[Does #4 mean #5 or #6? Are both okay? It is ambiguous, isn't it?]
2 answers
Really, 4, 5, and 6 mean much the same thing. I would interpret 6 to mean to look at the boy when I, too, am in the shop.