If the Defending Pokemon is Knocked Out by Dialga-G Lv.X's "Remove Lost" attack, is a coin still flipped to see if the Energy attached to the Defending Pokemon will be sent to the Lost Zone?
Yes, you calculate the damage dealt first, then flip for the energies to go to the Lost Zone, and finally remove any Pokemon that are knocked out.
Source: PUI Rules Team (2009-04-02)