An appositive is a noun or pronoun that identifies and / or explains another noun or pronoun in the same sentence. In this case, the noun is of the phrase is "Mr. smith". This noun is identified and explained by an appositive, which in the phrase is "our lawyer".
The expression "our lawyer" is identifying and explaining who and what Mr. Smith is.
Because a noun is a name of a Person Mr. Smith would be the noun or pronoun. An appositive follows a noun and gives further description, so therefore our lawyer is the Appositive.
