If I use an attack that says to "discard an Energy attached to your opponent's Active Pokemon" and I choose to discard their "Dangerous Energy" card, would I still receive the 2 damage counters from "Dangerous Energy" or not?
You would not receive the 2 damage counters.
Source: Ancient Origins FAQ (2015-08-13), TPCi Rules Team (2015-08-13)

Relevant cards

Note: All applicable cards may not be listed below.
XY7_82