Are you on the right layer? i.e. header vs. detail. Even if the controls show up when you open the layer its not always the layer that actually contains those controls, if that makes any sense. I wish you could click on a control and see the parent layer under properties in application studio, that would eliminate a lot of guess work.
To Alisa’s point, it looks like you’re in Job Entry.
You can add a control to that group when under the Details tab, but not the Main tab, which is what I suspect you’re in.