Look at your attack powers. In the Mouseover.
To clarify Chaos's answer: Compare the numbers for damage in the Manage Enhancements screen's tooltips both when slotted and unslotted. The boosts show up there.
However, if you slotted your attacks for maximum damage (3 Single Origins worth or more as a rule of thumb) you will get far less than 33% from the Alpha slot. A portion (the majority for now) of the Alpha slot gets hit by ED's diminishing returns. This is why I am of the opinion that it is better to Alpha slot for an attribute you haven't slotted for normally.
Champion 50s (blueside): Marc Bridge, Nicole Bridge, Fred Blaze, Colleen Storms, Sun's Chariot, Moon's Huntress, Point of Pride
Guardian 50s (redside): Connie Mand
AE arc: Spirit Plane Invasion, #29282, @Honbrid
Note that you will NOT be getting a 33% boost to your damage, unless your powers were underslotted for damage in the first place.
If you slotted the Common Boost, most of the enhancement will be consumed by ED, leaving only a 5-6% damage boost once ED applies to the portion affected by it.
With the Uncommon Boost, you'll get a 11% boost that ignores ED, plus however much of the remaining 22% gets past ED. Most characters will see a 11-13% boost on powers that were slotted to the endurance threshold, or roughly the equal of a small red inspiration.
Once you get the Very Rare (which isn't available yet), you'll have a 45% boost, 2/3 of which ignores ED, or a 30% boost plus 15% that's affected by ED. In this case, most characters will see a 30-33% boost, roughly equal to a large red.
@Roderick
I have my first slot filled with the muscular one for damage on my lvl 50 blaster. How do I know I am getting the 33% percent bonus on all my powers that deal damage ??? I really can't tell the difference between having it unlocked and slotted and before as my damage output seems the same. Not a number cruncher here so a basic explanation will do and maybe advice as to where to look to see where the bonus is being applied. Thanks.
Keeping it Brutal !!!!!!!!