You have to find the original view to edit that. In this case go to: Sales>Configuration>Address Book>Bank Accounts. You can find debug menu there. I'm not sure why some pop-ups don't display debug mode, but if it's another object you can find the object in some menu.

If you can't find the menu, you can do this:

1. Activate Developer Mode
2. Go to the form that you want to edit
3. Place your cursor over some field and look for 'Object' (In this case: res.partner.bank)
4. Go to Settings>Technical>User Interface>Views
5. On search box write the object model (In this case: res.partner.bank)
6. Select 'Search Object for: ' (In this case: 'Search Object for: res.partner.bank')

And you will find there all the views.

Note: Sometimes you are not going to find everything here because by code there are other ways to add some fields.