knife tool 2.8- used in past with no problems Vertices are not appearing when I drag with the knife tool across the object in edit mode. Am I missing a toggle somewhere? I would include a picture/screenshot but wouldn't really show you anything except knife hovering above the object.  I have used this tool with no problem before and I am thinking maybe there is something disabled that is critical to the tool.
In blender 2.8, the knife function does not work in view clip start 0.001, try to fix it to 0.01.