I set-up a View in my Forms Database that basically mimics the Monitor Page in Forms.  This can be easily searched for Tasks that are currently assigned to specific users or to generate reminder emails to staff.  I then set-up a process in Forms that loads that information into a table based on a user selection from the drop-down.  I use this to allow our managers to review what is currently assigned to their staff without having to give them admin-level access to see the Monitor page.  But I also use it to quickly see everything assigned to an employee upon their exit.  I posted about it previously on this page: https://answers.laserfiche.com/questions/164695/search-active-forms-processes#  But I think I may have changed the query a bit since then, so I'd be happy to share the current version if you'd like.

As far as finding processes that assign tasks to particular users (if the user is hard-coded on the task, and not being assigned via a variable), something like this should help identify them: 

SELECT 
  bp.[name] AS process_name,
  step.[step_type],
  step.[name] AS step_name,
  step.[definition_json]
FROM [LFForms].[dbo].[cf_bp_steps] AS step
LEFT JOIN [LFForms].[dbo].[cf_bp_processes] AS bpp ON bpp.[process_id] = step.[process_id]
LEFT JOIN [LFForms].[dbo].[cf_business_processes] AS bp ON bp.[bp_id] = bpp.[bp_id]
WHERE step.[definition_json] LIKE '%username%'
  AND step.[is_deleted] = 0
  AND bp.[is_deleted] = 0;

Workflow on the other hand is a whole other animal, and I don't personally know any tricks for finding stuff that is hard-coded to a specific employee.