Knight:

• nom pl. azantyssy
• acc pl. azantī

Guest:

• nom pl. zentyssy
• acc pl. zentī

This is in the nominative case because the verb to be / sagon preserves the nominative case. (This happens in some natural languages too, for example, German.) sagon is seen here as issi (the third person present tense plural / they are ).

Eight cases:

• nominative
• accusative
• genitive
• dative
• locative
• instrumental
• comitative
• vocative

Pattern for nouns ending in -ys: https://wiki.dothraki.org/High_Valyrian_Noun_Declensions#Solar-type:_loktys

The eight cases and their uses, the nominative case in this sentence is indicated on the wiki where it says "nominative ... other uses ... nominal predicates": https://wiki.dothraki.org/High_Valyrian_Noun_Cases