The sentence that contains a correctly punctuated nonrestrictive modifier is the following one: Jake, who is twenty-seven, is studying to be a yoga teacher. Nonrestrictive modifers contain information which is not essential to understand the meaning of the sentence and therefore can be dropped without changing its meaning. As this information is not relevant, it is "hidden" between commas.
Jake is studying to be a yoga teacher
As you can see, the modifier has been removed and the sentence is still grammatically correct. Sentence 2 is separating the complement from the verb (is/twenty-seven). In sentence 3, the verb to be is separated from its complement (twenty-seven) and in sentence 4 the auxiliary (is) is separated from the main verb (studying).
