One thing I always point to is John Gilliam’s excellent article War and Chivalry in the History of William the Marshal, which is an examination of what “chivalric warfare” looked like in practice, according to the biography of “the greatest knight in the world”. Spoiler alert: it does not look anything AT ALL like what a modern person would call chivalric.

There is also Geoffroi de Charny’s “Book of Chivalry”, which is an actual 14th century knight writing to explain what he thought chivalry should be.

However, note that the context of these sources are a few centuries apart.

It depends exactly what you want to know; this is a broad topic covering at least 6 centuries and many countries. Also, there is no one "Code of Chivalry"; there are many, and variously adhered to.

Geoffroi de Charny's A Knight's Own Book of Chivalry, ed. Elspeth Kennedy, is one knight's attempt to formulate a coherent code of chivalry. But I would suggest starting with something broader and more basic, like Richard Kaeuper's Medieval Chivalry.