If you want to manually check this, and have versioning enabled then you could check the version history. If you want it covered in the workflow, then you either:
use hidden (Nintex ?) form fields/columns to keep track of the previous values. At the end of the change triggering wf you copy all the required fields into these prev_value fields.
create a simple kick-off workflow per changed column for the real workflow (no longer triggered by change event). So WF_Field01_Changes, WF_Field02_Changes etc (starting if pref value of field has changed compared to the current) which then call WF_MyWorkflow. Only of interest for small lists