Can a character with MOTF2 use 2fp to move an extra 4 squares during thier movement phase? I know Knightspeed and Master speed don't stack, but hiow does the generic +2 movement addition work?

It works as you described. For example, Loda can spend 3 force to move 6 extra spaces for a total of 12 and still attack. Luke CotF (assuming Obi or Yoda has given him spirit) can use knight speed with extra move for the 12 as well.

Now if you really want to get crazy, combine Luke CotF (with spirit) with Han Stormtrooper. That's a 16 square Auto Crit or 18 square move and attack

I'll have to remember that the next time I use Loda. I didn't realize I could use the regular +2 movement multiple times.