I kind of feel it was both of them screaming. Despite that Tom had been a controller for so long and in book #6 when Jake gets Tom's memories or thoughts or whatever it was he says Tom spent his time wishing he could die, I doubt when the time really came he really did – especially with the end so near. But yeah, like what you said I think both Tom and the Yeerk was scared and screamed out for Jake to help.
ACTUALLY IDK. When you said:
Were the thoughts of Tom and his Yeerk so alike at that moment that they both wanted to yell exactly the same thing?
That interested me because I sort of feel like maybe Tom would have understood why he was being killed. I mean he knew Jake and, according to the plot, the only way for the Animorphs to have won the war = Tom/his Yeerk had to die, so he probably knew Jake had to do what he had to do to win the war. I mean even when he screams out for Jake to stop Rachel from killing him, he had to have known he was the one who sent her. Yeah I know I'm contradicting myself, but as I said idk, now I'm thinking about it too much D:
That quote always gave me chills though. It was really sad and upset me but made sense too.