If I use Ambipom [G]'s "Tail Code" attack to move an energy card from the Defending Pokemon to one of my opponent's Pokemon that has an Unown-G attached to it, what happens?
While Unown-G prevents the attachment of the energy to the protected Pokemon, it does not prevent the removal of the energy card from the Defending Pokemon. The energy card is discarded.
Source: PUI Rules Team (2010-01-14)

Relevant cards

Note: All applicable cards may not be listed below.
HGSS2_43
PL1_48
PL2_56