You cannot add a second questionnaire that would be specific to lower-limb but you can easily add a lower-limb category and related questions / answers. Here is how:

Step 1

Rename 'Sleep quality' category to 'Sleep' and replace 'Sleep quantity' by 'Lower Limb comfort' (or the name of your choice) and save the questionnaire

Step 2

Associate all sleep questions to the new 'Sleep' category

Step 3

Go at the end of the questionnaire, click on the green cross and add your Lower limb questions

Step 4

Save your changes