1ADV [ADVERB after verb]在其上Thereon means on the object or surface just mentioned. 在其上 [formal]
There was a card on each door with a guest's name inscribed thereon.
每扇门上都有张卡,上面印着客人的名字。
2ADV [n ADVERB, ADVERB after verb]就此;与此相关Thereon can be used to refer back to a thing that has previously been mentioned to show that the word just used relates to that thing. 就此;与此相关 [formal]
You will, in addition, pay to the Bank any losses, costs, expenses or legal fees (including VAT thereon).