Do you have 'Advanced' Tools' enabled? Go to Preferences (which in the latest version is now called Settings) > Advanced Tools. In the Advanced Tools window, enable Show Advanced Tools and enable all of the options. Assuming you now have Advanced Tools enabled, Logic should autodetect the KL88 as a control surface when you first connect it and ask you if you want to autoassign the controls. If it still does not do that, you need to add it as a control surface inside Logic through Logic Pro > Preferences (or Settings) > Control Surfaces > Setup.
I am also assuming you have the KL88's own preferences set to DAW mode and have chosen Logic Pro as your DAW.