Why isn't this using הכירו? Is this telling us to "biblically" know our enemies? Or is this phrase an exception to the norm?
From the notes on the Present 1 lesson: "The important thing to note is that using לדעת about a person means to "know" them in the biblical sense - so be careful not to use it about something alive unless that is what you actually mean."
When I looked for the phrase "know your enemies" in reverso, almost all occurrences were with ידע instead of הכיר. My thinking is that it is either just a set phrase that doesn't necessarily mean knowing them biblically, but rather thoroughly, so that you might anticipate their move. Or that it conveys the meaning: know who your enemies are.