Most of Keystone's trailers that use steel wheels have "lug nut covers" installed. Almost always made of plastic, some are black, some are white and some are chrome. They simply "push onto" the lug nut to "make it pretty"... They serve no practical purpose (other than to maybe keep dirt off the lug nut and threads).
Usually you can pull them off with pliers or use a flat blade screwdriver to get behind them and "pop" them off. There is a "special tool" available to remove them. If you're "mostly left thumbs" it might be a good idea to get the tool rather than "destroy those plastic caps" with a set of "clutzey pliers"....
Here's one link to the type of tool you'd need: https://www.iowa80.com/pd/universal-...FQqPaQodt14MFA