After incident created, In view mode if we change the “Priority” field value the custom field named “Work notes” should be mandatory or need to restrict before updating the incident.
No, this is not possible out of the box as you describe. The only add-on that I am aware of that could do that is ScriptRunner Behaviours app.
However, you could add a Validator to a transition in your workflow (or multiple transitions) so that the field is required to transition the issue if the Priority field is a certain value.
Sure - Create two transitions from the status A to status B where you want to check the field. Place a Condition on one of them where the Priority field = whatever value that will trigger the mandatory field. While there, add a Field Required Validator to that same transition that the Work notes field is required.
Next add a Condition on the other transition from A to B where the Priority field != to the value.
