The weakest job becomes the strongest in the world with past life knowledge is a Manga/Manhwa/Manhua in english language, REINCARNATION series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

A young wizard dominates with the knowledge from his past life, breaking through level limits! The strongest wizard, Roy, is reincarnated into the future as a young boy, Yuug. However, magic has declined since then, and wizards are considered the weakest class. With the knowledge of magic from his past life and his extreme-level abilities, Yuug embarks on his second life's adventure...