show.obj(VIEWNO);
Cel 0 of loop 0 of view VIEWNO is shown at the bottom of the screen, with the view's description displayed above. Both dissapear when a key is pressed. The view does not need to be loaded in order to use this command.
The command does not actually have anything to do with screen objects (which are normally referred to as just "objects"). It is meant for when the player examines an inventory item - each item should have a view with a picture of it and a description, which is displayed using show.obj when the player examines it. Inventory items were sometimes called "objects", which is why the command was called show.obj.