How to use knife tool inside modeler
To use knife tool inside modeler
Multiply > Knife or press shift (k)
If you would like to use Knife tool inside the modeler, first you need to select the Knife option from the Multiply menu. The Knife tool allows user to create a new slide of point on the object. What you need to do is just simply drag out a slicing line in any view port and no image is needed at the background layer. The line is infinite along the axis perpendicular and if you wish to the view it, just drag in.
You can also press shift (k) command key to select knife tool.