Can we enable dependent field after an approval in a work flow

Just needing some clarification to properly answer your question. If I am understanding it correctly, the ticket is being submitted and then awaits approval in the process section. Once approved, you are wanting a field to appear with a checklist of things to do? But you don't want that field to appear until the approval has gone through...I think that's what you are saying? Correct me if I am wrong.

Yes, you understood it right. 

Below is the scenario. 

The client has a process where, the end user requests a replacement of laptop,desktop or any hardware. 

It goes to the requestor's manager to approve which is direct manager approval. 

once approved, the request comes to the technical team to validate the checklist of items such as

Lifecycle of 4 years

Broken beyond repair

Replacement of spare will fix the issue

Out of stock in which case the case is is put on hold and a PO is issued.

If I have this field enabled after the approval, I want to use this further to create a PO workflow..

Condition if the field Out of stock, Start the process of PO notification or PO approvals.

This goes also like, if Out of Stock or Instock.. If Instock, fill the replacement sheet with Old hardware details and new hardware details. 

Okay that makes sense. I am not sure that you can do field dependency for the assignee. You can make a workflow in the process that lists tasks for the assignee to complete based on conditions you set, but it sounds like you already knew that. It would be more manual than automated but it would be an okay temporary option. I tried looking at several automation rule options and dynamic form options, but I just couldn't make anything work to where it triggered the fields and workflow the way you wanted. Wish I could have helped more! Hopefully someone else will be able to help.