These are as follows:
Flip Green: Here you can change the axis in the dropdown to match the Normal/Derivative maps for your engine or application as required. By default Knald is set to X+Y+Z+, so if you are using a Normal or Derivative map that differs from this configuration, you will need to change this setting. To change this setting check the Flip Green check box to save your choice.
Bump Scale: The global strength of the processed Normal and Derivative maps.