In this puzzle you first have to randomly tap around the wall to find Q1, Q2, Q3 and Q4. You can find:
Q1 on the top right of the wall.
Q2 on the top left of the wall.
Q3 on the bottom left of the wall.
And Q4 on the bottom right of the wall.
Now, tap the areas of the wall in the order shown at the top. This will reveal a key which you can use to exit this level.