সহায়িকা

Explanation
The phrase "one of" requires a plural noun ("friends") after it, because you are choosing one person from a group of many people.
However, the subject of the sentence is "one" (which is singular), so the verb must be singular ("is") to agree with the subject.
Additionally, the profession should be introduced with the singular indefinite article "a" because it refers to a single individual.
Why other options are incorrect
. One of my friend are lawyer is incorrect because it uses the singular noun friend (should be friends), the plural verb are (should be is), and is missing the article a before lawyer.
One of my friend is a lawyer is incorrect because it uses the singular noun friend (should be friends).
One of my friends are lawyers is incorrect because it uses the plural verb are (should be is).

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