Question

find the relative clause. if it is nonrestrictive, set it off with commas. if it is restrictive, submit the text without making any changes.
the statue of libertys crown which houses a popular observation deck commands an astounding view of new york citys expansive skyline.

Explanation:

The relative clause "which houses a popular observation deck" provides extra, non-essential information about the Statue of Liberty's crown (the crown is already uniquely identified, so the clause doesn't restrict which crown we mean). Nonrestrictive clauses are set off with commas.

Answer:

The Statue of Liberty's crown, which houses a popular observation deck, commands an astounding view of New York City's expansive skyline.