My best guess is to go to a sprite animation editor and create an animation that make the character to feel like knock back and then do your variable and speed and placement.
Best guess here is to use spriter pro there a free mode and you can basically just animate him going back and then once you are done.
In the contruct there a great powerful tool call the slider. Now make two value 0-999 Next reference the pixel action that you wish to do and then create a textbox. Now I want you to do something like reference the pixel knock back variable to the value of the slider value so that you can dynamically change it in game without changing it in the event every 2 sec. and to make it visually easier to see the number is to set the text box to every tick - set text to the slider value.
And this should give you a sort of a turning knob to see what pixel speed and animation would this look good but does well visually. I use this technique when i have a problem with speed and animation. dunno why there isnt a tutorial on this hint. but basically what you want depend on your eyes. but this is just my idea on how to help you out. i dunno what else i can think of