The underlined word 'yes!' identifies to interjection as the part of speech.
Interjections refer to the part of speech which conveys a sentiment or an emotion such as disgust, surprise, excitement, joy and so forth. Grammatically it is not related to the part of a sentence. Usually, it is used at the beginning of the sentence to express an emotion or sentiment.
Therefore, in the above sentence, 'yes!' with an exclamation mark indicates joy or happiness for jambalaya being prepared in the kitchen.
