Guild Wars 2

How exactly does it work?
Do I need a target for it to function or does it reveal everyone around me?

Targeted. Also note that using any command, such as F skills or other shouts remove the effects of Sic ‘Em from the pet. For example use Jaguar F2 stealth first, then Sic ’Em if you don’t want to lose the extra dmg boost.

Why don’t you just test it?
But here is the answer anyway
Your target will get the reveal debuff as soon as you use the ability.

You need a target. Then it applies Revealed to that target, and a status effect buff to your pet. If you issue any other commands to your pet, the Sic Em buff will be removed from the pet.

I always found this skill insanely stupid … It only prevents one from stealth but it would be much more interesting if sic em would autoamticly reveal all stealthed targets around the pet ~360ø. Why should my doggie not smell an invisible target!?