The terms of a confidentiality agreement, including its length or duration, are as set forth in the agreement itself: the law does not specify length, but rather it is whatever is set forth in the agreement. Therefore, there is no way to know the duration without seeing the agreement.There is no way to get the agreement without asking  for it from the employer--it is not kept or filed any place else. In terms of invalidating it, a contract--including a client confidentiality agreement--is only voided by fraud (i.e. the other side intentionally lied to you about something material, or important, to get you to sign the agreement) or "mutual mistake" (you and the other side each thought the agreement meant something other than what it did--but both sides must have been in error about the agreement); or it can be terminated if the other side breaches or violates a material, or important, term of the agreement. But apart from this, the agreement will be enforceable as signed.