The wizard is, as always, something of a glass cannon. Is there a skill the provides the greatest knockback for the purposes of crowd control? If there are two (one for single targets, one for multiples), please list the conditions in which they would best apply.
Your best bet is Wave of Force with the Impactful Wave rune.
Wizards don't have a skill that will reliably cause Knockback. If you're finding that enemies are closing on you quickly, try dropping a Slow Time with Miasma or Blizzard with Grasping Chill or Frost Nova with Shatter. These aren't Knockback skills, but they do slow/freeze very well, allowing you to flee or attack with impunity (for a second or two).