In a dot and cross diagram you show the new positions of the electrons after chemical bonding as taken place between two elements. In covalent bonding the electrons are shared therefore the atoms will overlap one another to show the sharing of the electrons. In iconic bonding the electrons are transferred so the the atoms will be next to one another to demonstrate the electrons transfer to the other atom.
The bond between hydrogen and fluorine to make hydrogen fluoride is covalent as it is a bond between two non-metals.
The bond between potassium and fluorine to make potassium fluorine is iconic as it is a bond between a metal (potassium), and a non-metal (fluorine).
As I am unable to post images here, I have provided links in the sources below to the two diagrams for Hydrogen fluoride, and Potassium fluoride that already exist on the internet.