Knights in original and dubbed material tend to take on characteristics that mix formal modern language and bushigo, i.e. pop-fictional samurai language. Thus nearly all of them use watashi as their first person reference, they will switch to something far more samurai-esque such as soregashi, when being extremely formal towards a lord, lady or monarch. Hence there is a distinct historical colouring, if affected, to convey how these medieval nobles talk.
The manga Berserk has no shortage of knights, and Azan, the monk-knight more or less serves as a perfect example. Beyond his rotund, but robust frame, he sports a gentlemanly moustache and has a massive pole-arm as his weapon of choice. He manner of speaking however is very reminiscent of samurai, preferring sessou (拙僧, "clumsy monk") and gusou (愚僧, "foolish monk") as his main modes of referring to himself, something paralled in the warrior-monks of Japanese pop-culture and cinema. Case in point, when he fights the main character in a duel, he introduces himself in this manner:
我は聖鉄鎖騎士団副団長アザン！！ 字を鉄棍鬼アザンと申す！！ 黒い剣士よ いざ尋常に勝負！！
Ware wa seitessakishidan fukudanchou Azan! Aza wa tekkonki Azan to mousu! Kuroi kenshi yo. Iza jinjou ni shoubu!
"I am vice-commander of the Holy Chain Knights, Azan!! My epipthet is Azan, the iron-cudgle demon!! Black swordsman! Huzzah! I challenge thee to close quarter combat!"
Here he uses 我 (ware), a first person pronoun of Old Japanese stock, for theatrical effect, when proclaiming his name and title, along with using the plain form of 申す (mousu, "to humbly state/report/say/do"), which further adds to his archaic flavour. Lastly he uses the stock phrase いざ尋常に勝負 (iza jinjou ni shoubu, lit. "Now then, [let us have a] regular bout of combat"), which has become famous as the sound first heard prior to any match in the Samurai Shodown series of fighting games.
Elsewhere he uses regular keigo, albeit with archaic pronominals such as おぬし (onushi, "thou"), そなた (sonata, "thou") and 貴公 (kikou, lit. "esteemed duke") the latter being a more formal and elevated mode of second person reference. One extremely favoured by the knights of From's Souls series as well as countless other fantasy themed games and media. "Onushi" and "sonata" are both semi-informal and still imply an air of respect from the speaker towards their audience, though "onushi" could be regarded as the most informal, akin to a modern お前 (omae).
It should be noted that knights in English, too, stereotypically speak some quasi variety of Shakespearean or Chaucerian English – paralleling the affected archaic tone in the Japanese fiction.