What enchantment should I get for a whip

[kreynolds]

So when I get BAB 6/1 I can attack with my Brill nrg whip, knock em out(Sub dmg) and Coup em' on the 1? And I'm only dual weilding if I go 6/1/-2(or what ever right?)

No. To use both of your attacks, you must take a full-attack action. A coup de grace is a full-round action, unless you have the Death Blow feat which shortens it to a standard action, so you don't have enough time to pull it off in the same round that you attack.