For example, if you one-hit KO a Pokemon and get, say, 65 Exp., and then knock one out in two moves, would you receive more/less Exp. points?

The only factors here are growth rate and EXP yield. Amount of moves has nothing to do with it. Other external factors are: Exp. power in BW/BW2, Exp O-Power in XY/ORAS and the Lucky Egg. Hope this helps!

No, The amount of moves don't matter. Exp differs by growth rate. Say you are training Pokemon in granite cave. Ralts beat a makuhita and gain 100 exp. points. The exp bar moves just a little bit. But if you're training Taillow and it gets 100 exp. points, then the exp bar will move by a lot.