The trick with the prod is to get VERY close. Unlike RtCW, you can "bump" into the back of a guy without alerting him. If you're right behind them, a single prod knocks them to the ground.
And yeah, in the nanotech lab of Mj12, I crept up behind the MiB in his chair, knockd him out and looted him! Yay!

I think you can reclaim knives after you use them. I've certainly done that with darts - pick the ones that missed out of walls, and sometimes they are in bodies.