When opponent's warwick enter and I have emperor divide in hand. Can I use emperor divide from my hand to escape warwick kill ability?

No — not from hand. Emperor's Divide in hand is only an [Action] spell, and once Warwick's attack trigger goes on the chain the turn is in a Closed State, where only [Reaction] cards can be played (Rule 309.1.a). Warwick's "when I attack, kill all damaged enemy units here" trigger is added to the initial chain of combat, so your only window there is reaction speed.

Note there's also no window earlier: playing Warwick gives no reaction opportunity (permanents auto-resolve), and he's already an attacker with the trigger on the chain by the time a showdown opens, so you never get an Open State to play the Action before the kill resolves.

If you had hidden Emperor's Divide earlier at a battlefield you control, it would work — from Hidden it gains Reaction and plays for [0], so you could respond, moving your damaged units to Base; they're no longer "here" when Warwick's trigger resolves and so survive (same logic as FAQ #3645).