Learn Turkish: Şurası bir park mı?

Şu usually means "that" and is placed right before a noun, like in şu park (that park). When you want to refer to a specific location as a noun meaning "that place," you use the pronoun şurası.

Where is the word for "is" in this sentence?

Turkish doesn't have a separate word for "is" in simple present sentences like this. Stating the subject (şurası) followed by what it is (bir park) naturally creates the "is" meaning.

Why do we need the word bir here?

While Turkish sometimes drops bir (a/an), using it here makes the sentence sound complete when asking if a specific location belongs to the category of "a park". It functions exactly like the English article "a".

Why is the question particle mı instead of mi?

The question particle changes based on the 4-way vowel harmony rule. It looks at the last vowel of the word right before it, which is the "a" in park. Because "a" is a back, unrounded vowel, the particle becomes mı.