Questions & Answers about Jaka jest ta książka? — Bardzo dobra.
Why do we use jaka instead of jak here?
Jak usually means "how" (as in jak się masz? - how are you?). Jaka is a question word used to ask "what kind of" or "what is it like" about a feminine noun. Because książka (book) is feminine, we use the feminine form jaka instead of the masculine jaki or neuter jakie.
I learned that "this is" is to jest. Why does this sentence use ta instead of to?
Why is the answer just bardzo dobra? Shouldn't it be ona jest bardzo dobra (it is very good)?
You can absolutely say ona jest bardzo dobra, but in Polish, it is extremely common to drop the pronoun and the verb in short replies. Because the question just asked about the book, replying with only bardzo dobra (very good) sounds perfectly natural and conversational.
How do I know that dobra is the right word for "good" here?