The possessive form of the proper noun Cox is Cox's.
Example: This is Mr. Cox's book.
The singular possessive form for the proper noun Cox is Cox's.Example: Jeff Cox's brother is graduating this weekend.
To make a last name ending in S possessive, add an apostrophe after the S. For example, "Jones'" is the possessive form of the last name Jones.
Doc Cox's birth name is Robert Cox.
Zaco Cox's birth name is Zac Alexander Cox.
DeWayne Cox's birth name is De Wayne Cox.
Dick Cox's birth name is Elmer Joseph Cox.
Doran Cox's birth name is Cox, Doran Henry.
Eva Cox's birth name is Eva Maria Cox.
Gerard Cox's birth name is Gerardus Antonius Cox.
Lara Cox's birth name is Cox, Lara Jane.
Nikki Cox's birth name is Nicole Avery Cox.
Noel Cox's birth name is Russell Noel Cox.