What does camping Zhang Wansen want to ask Chen Beihang?

When camping, Zhang Wansen wanted to ask about Chen Beixing Lighthouse.

According to Douban movie query, in the TV series "Twinkle, Twinkle, Bright Stars", Chen Beixing and Zhang Wansen met Gray's people while camping. In order to protect Chen Beixing, Zhang Wansen was killed by Gray's men. Chen Beihang accidentally traveled back to the past. After the college entrance examination, he went camping with Zhang Wansen, during which he asked about the origin of Zhang Wansen's lighthouse, but Zhang Wansen said it was a secret.