If I have Strong Energy attached to a Fighting type Pokemon and use an attack that says to discard an energy, do I get the bonus damage from Strong Energy before I discard it or not?
Yes, you do.
Source: Furious Fists FAQ (2014-08-28), TPCi Rules Team (2014-08-28)

Relevant cards

Note: All applicable cards may not be listed below.
XY3_104