If variables section not visible in the HR case form, then we need to open the HR case form and follow the below steps:

a. open Form Layout

b. You will see slush bucket with available fields

c. If you can find "Variable Editor " in the right side slush bucket, then you will save and exit. Now the variables section will be shown. 

d. Else, Bring Variable editor from the left slush bucket to right slush bucket. Then save. Now you will observe, it will show the Variables section in the HR case form..

Note: Variable editor should be created on "sn_hr_core_case" Table.