Pop-up window with comments

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Hello! I am struggling with the task to provide a pop-up window with the comments once an existed sales order open. I have created a window and an action. Now, I need to write a script with a trigger. Here is the challenge. Once a user chooses an existed sales order, the script should check if there are any comments. If there are comments, a pop-up window with those comments should appear. Does that sound feasible? Thanks.