Say this is the setup:

xxxLxxx
xxxxJxx
xxxxxxx
xxxx1xx

x: clear terrain
L: enemy Lackey
J: enemy Joker
1: friendly fig attacking Joker

If 1 succeeds in hitting Joker, and rolls doubles, but Joker passes the damage off to Lackey via Mastermind, does the Lackey get knocked back? If so, what direction? In a straight line from the Joker, or in a straight line from 1?

The Lackey receives knockback away from figure 1.