Modifying column so certain groups can't view it

Hi qhenry 

It is not possible to securely hide columns to some people. 

What I would suggest if possible in your scenario is to have a different list for the comments that only those who are allowed can access. 

In SharePoint you could solve this by using javascript for example:

On the ticket list you can add column that contains hyperlink "add comment" that will open "comment" dialog for those who are allowed to and bind it together on the ticket itemid so each comment has a reference id to the ticket. Then maybe you could add another column to the ticekt list that contains hyperlink "Show all comments", that action would query the comments list by ticket itemid.  

Or you could do same thing on the item view form by adding button or link with script editor.

And I'm sure you can solve this in a similar way in PowerApps for example when you view single item you add extra action or controls if current user is allowed to see it and then submit comment to different list.