Abilities » Toolbox
If Sigilyph with the "Toolbox" Ability has Plasma Badge and Reversal Trigger attached, do I get to search my deck for a card when it is KO'd by an attack?
Yes, you can. The tools are still present on the Pokemon when it's KO'd (assuming the attack does not discard the tools first), so you would get to use the effect of Reversal Trigger since Plasma Badge makes Sigilyph a Plasma Pokemon.
Source: TPCi Rules Team (2013-08-15)
Abilities » Toolbox
Can you attach more than one tool of the same name to Sigilyph with the "Toolbox" Ability? And if so, do the effects of the tools stack?
Yes to both questions.
Source: TPCi Rules Team (2013-08-15)
Abilities » Toolbox
If Sigilyph with the "Toolbox" Ability gets attacked with something that discards a Pokemon Tool who gets to choose which tool gets discarded?
If an attack says to discard a Pokemon Tool it will discard all tools attached to that Pokemon, not just one. So poor Sigilyph would lose all of his tools.
Source: Plasma Blast FAQ (2013-08-15), TPCi Rules Team (2013-08-15)