It really depends on what the UI currently looks like. And what version you are using. And the nature of the information, as I think about it.
If the information is something unusual (credit hold, special VIP, birthday, whatever) then you might want a separate window to show up. Typically that isn’t very good UI, though unless the user closes it right away like an alert.
Better would be to have a hidden variable(s) or subform on the regular form that is used to display such information.
Or you could pop open an alert with a short headline like “Credit Hold!” which the user closes right away and the details of it appear in the hidden area. This gets the user’s attention to the situation and they can look at the details if they need them. But you could also accommodate that effect by adding a ‘headline’ var at the top of the form, in red and the details appear in the hidden area. This is less intrusive than a popup if you are scrolling through a list.
If you do decide to have the second window open you have to manage closing it again.
When a client says “I want a popup for this” they may actually need a popup. But it’s worth a little conversation to determine exactly what task they need accomplish and then decide if a popup is actually the best solution.