It is done using the ManagerLink on the Employee record. This is a link field back to the employee record so you can set a manager for a user, it is also possible to populate from AD (if AD has managers set).
For the Approval on the request offering, I pull the manager recid on to the offering form the employee lookup or CurrentUser functions. This can then be used directly on the Approval in the User from Context BO field/ Service Request Parameter field.
I have a similar issue with the "Get Approval" block. I had no problem with a manager approval by storing the manager's email in a hidden form field triggered by
My problem now is with how do I send the approval to the HR Team? There doesn't seem to be a way to do this unlike a Task block that has a team drop down list to select from.