2 part survey that needs to be completed by different people

You have to do this using two concepts:

1) trigger email: once the employee fill the survey send a trigger email with the Recontact link to the HR.
2) Recontact link: with the Recontact link data is stored as a single record for both part.

3) create 2 blocks in survey one for employee and one for HR, and for employee append your link with say employee=1 like link?employee=1
For hr use link like retake link?hr=1. Put these 2 blocks in branch logics with employee=1 and hr=1