This is going to sound crazy, but does Alexander Luthor Junior have his dad's brain? Where can I read more? Thanks.

Is this a Post Crisis comic?

I think he's referrring to the time Lex Luthor posed as his own son in a cloned body during the 90s (so yeah, post-crisis)

Lex's original body had aqquired a form of cancer due to exposure to the Kryptonite ring he wore at the time, so he faked his death and underwent an operation, and his brain was transplanted from the cancer-ridden body to a freshly cloned one. He returned to Metropolis as "Alexander Luthor Junior", Lex's "son".. Lex's cloned body ultimately started failing him though, and it drove him insane. Lex was eventually rejuvenated in Man of Tommorow#1 and returned to his normal self. He was aqquited of all crimes he commited in his cloned body (like launching an attack that crippled Metropolis) by blaming the incidents on a "rogue" clone that posed as him

@zariusii: Oh that I should have guessed as such.