The parts of speech for the words in the sentence are:
<em>Jim:</em> noun. A proper noun
<em>who</em>: pronoun. A relative pronoun, refering to the subject Jim and Tiffany.
<em>favorite</em>: adjective. A word to describe cousins in this sentence.
<em>just </em>- adverb. Adverb of time - short time before now.
<em>cutest</em> - adjective - to describe dog.
<em>running</em> - verb - word that expresses action or state.
<em>their</em> - adjective. Possessive adjective (possessive dederminer)
<em>behind</em> - preposition (of place), showing the position of the dog.
<em>the </em>- article - definite article, refering to a car that is already known.