Whereon means 'on which'. It points back to a surface or a base already named and tells you what sits or happens on it: 'the table whereon the bread was placed' = 'the table on which the bread was placed'. It can also mean the ground on which an argument or a claim rests: 'the principle whereon the whole plan is built'. Once in a while, in old narrative, it means 'at which moment, whereupon' — 'He gave the signal, whereon the doors opened' — but the word that really does that job is whereupon, which is still used today in storytelling and formal accounts. Whereon itself is the rarest and most old-fashioned member of this family: Bible, poetry, old legal writing, and little else. Nobody speaks it. Say 'on which' in formal writing and 'that … on' in speech.

在其上（古語）。等於 on which。比 wherein、whereby 更罕見，只在聖經、詩、古法律文件裡出現。要講「接著就……」用的是 whereupon，不是 whereon，兩個別搞混。