Ctrl + Space

i'm confused on what this combination does. is there a way to make a henchman attack an aggro without me moving into the aggro's range?

That is how you call your target to get your henchmen, pets, and real-live players (if they are paying attention and clicking "t") all to attack the same target. If you can see the enemy's name in red, you can initiate the attack - you do not have to be in range.

You will see your character attempt to get in range, but you can easily just control that again with the w, a, s, and d.

Or you can do the correct way and press shift+ctrl+space.