To open or close the debug panel press CTRL + SHIFT + F12. Note the debug panel contents can change regularly as things are moved around (to/from options, to/from console commands).
Alternatively search for it in the options to toggle it on and off:
Several of these options are good for checking advanced textures such as in the Standard material inputs and will demonstrate the nature of the different ways the engine loads textures, eg: Material Metallic can show the shiny metal bits of things:
While the normals view shows the normal bumpmap textures: