Answer:
George's father wrote "What time?" on a spy club meeting poster.
He is asking about the time of the meeting because he says he doesn't see how he was supposed to go to the meeting if they don't write the time, but he only wrote the question in fun.
Step-by-step explanation:
Liar and a Spy is about a boy named Georges who makes friends with a boy in his new apartment building at a spy club meeting, where he was made to spy on another neighbor.
The poster Georges' father writes "What time?" on is a notice for a meeting called by the spy club, which led to Georges' introduction to the club.