Where did Freak have a medical emergency?

In the school's cafeteria.

Explanation:

The young adult novel Freak the Mighty by Rodman Philbrick is about a young boy Maxwell Kane and his friendship with a physically deformed young boy Kevin who had Morquoi syndrome. The plot revolves around the two becoming best of friends and becoming one identity Freak the Mighty.

Chapter 13 is set in the school when Max got news about his father who has been in jail for life. After that, he and Freak went to the cafeteria where they had American chop suey. It was then that "Freak's face is all red and swollen up and he's making this huk-huk-huk noise. He can't talk, all he can do is look at me and try to say something with his eyes and then I'm running to get the nurse". This is the medical emergency that Kevin had in the school's cafeteria, allergic reaction to the gooey chop suey.