Jessica's Peeps Keith was with Lance when the power went out. He would've gone to check out on the rest of Voltron afterwards and was extra twitchy about finding out what was going on.
Tony Stark was hanging out with the Holts I think and... um.... IDK? I guess he was ok? He would've been worried about all the tech being out and not being able to connect to anything other than his suit and probably first focused on getting the power relay and tablets back working so communication can happen? IDK.
Nico di Angelo was with Anakin and would've gone to check on the other demigods once they were sure about Anakin's people.
Flash Thompson shot up to a ready fight stance (if a little shakey) wherever he was because of spider-sense going 'whoa something ain't right'. He probably went to go check on Credence afterwards considering their talks about the bad things that happen with his anxiety and all. >_>
Ben Reilly was with Loki and did the same jolt up ready thing before the EMP went off because his spidey sense was tingling. He would've checked to make sure Aracely was ok as well as any others he was close to in location before going into superhero help mode with Loki in tow.