when drops of lemon juice are put on blue litmus it turns red what will happen if we put some drops of soap solutionon the same position on litmus paper

Nothing will happen.

when soap solution is put on blue litmus paper there is no change

There will be no colour change observed on blue litmus paper. Since lemon juice is acidic in nature so it turns the blue litmus to red. Whereas soap solution is a mild alkali, there will no change in colour. It will change the colour of red litmus to red.