Is the a way to project surface cuts through the entire object? I am trying to cut this block mold at the lines I made.  The issue is that I can only cut the surface, and can't figure out how to cut all the way through, including the inner geometry.  Is there a way to project these lines through the entire object?
Use the Knife Project tool: https://docs.blender.org/manual/en/latest/modeling/meshes/editing/subdividing/knife.html#knife-project Make sure you turn on Cut Through option



.. Or the Knife Tool and hit Z key to make sure to turn on Cut through: