He earned nothing: he was an apprentice. He started out as an errand boy for Ribeau's bookshop and after that trial then was taken on as an apprentice. Silvanus P Thompson, in his 1898 Faraday: Life and Work quotes from the indenture that the apprenticeship was "without premium". That meant that Ribeau was to feed and clothe him and teach him the trade, and the premium was the amount Faraday's parents would normally have had to pay to have him apprenticed- so Ribeau obviously had decided Faraday was a good addition to the shop ( there also were usually some other conditions about the apprentice being obedient and not getting married, the master educating him, making sure he went to church...) . It's quite possible that Faraday was given a bit of pocket money from time to time, or allowed to keep a tip from a customer. But apprentices were not paid laborers- they paid for their learning with their labor.

Thompson states that when Faraday expressed the hope of not becoming a tradesman, Sir Humphrey Davy engaged him to be the laboratory assistant at the Royal Institution in 1813 at the rate of 25 shillings a week, and Faraday was given a room to live in as well. That was the same as the previous laboratory assistant had been given.

Thompson's book is over on Project Gutenberg here.

The Royal Institution has digitized Faraday's papers and letters, and there may be more in them about his apprenticeship. However, there are several volumes and the fee for each is substantial.

https://digital-library.theiet.org/content/books/ht/pbsp021e;jsessionid=31menp0re5l9j.x-iet-live-01