YUM eat them!!!

Preferably you want the ones that are around racket ball sized or a tad smaller. The bigger they are the more fiberous.
You can eat them raw...as Ola does (YUM), or cut it up however you like and toss in pan with some salt, tad bit of sugar and butter cook them till softened yet still firm.
I'd say any way you'd cook up broccoli you can do kohlrabi, slaw, salad, steamed, gratin, rice, buttered...you name it.