If Temple of Sinnoh is in play, does Meloetta's "Melodious Echo" attack still do 70 damage for each Fusion Strike Energy attached?
Yes. Temple of Sinnoh removes all effects and provides 1 Colorless energy, but it does not change the card name to be something other than "Fusion Strike Energy". So Melodious Echo still does 70 damage for each attached Fusion Strike Energy you have in play.
Source: TPCi Rules Team (2022-06-02)

Relevant cards

Note: All applicable cards may not be listed below.
SWSH8_124
SWSH8_124
SWSH10_155
SWSH10_155
SWSH8_244
SWSH8_244