。
Chuu-tarou is Tanaka's dog.
Literal
Chuu-tarou [topic-は] Tanaka-[polite-さん] [gen-の] dog [copula-です].
Textbook identification sentence X は Y です. The dog's name is a made-up cutesy compound: チュー is the onomatopoeia for a squeaking or kissing sound, and ~たろう is a playful diminutive ending modeled on 太郎 (a stock boy's name) — together making a whimsical pet name. The whole sentence is trivial grammar, but the name encodes a typical Japanese naming-pattern joke.