ok, so if i have in play satellite hq location:
target jla attacker gets +x def this attack, where x is its willpower.
and jon stewart:
willpower 4. ally: whenever a character you control becomes powered-up, that character gets +2 willpower this attack.
If i attack and use the satellite to give def to a character, (lets say 4) will it increase to 6 when i power-up that character or it is set to 4 because i gave bonus earlier?

the DEF bonus is set when it resolves. so if you increase the WP of the attacker after that the DEF bonus will not increase. if you plan on powering up the attacker, wait to use the Satalite HQ untill after you power-up.

helpful as always, thanks