In New York State what is the potential marital asset value of a spouse who has become a RN during the marriage and previously worked minimally.

The question isn't the value of the RN, but the enhanced earnings capacity it generates. To calculate one looks at what the individual was doing before becoming an RN, what the salary was, and compares it to the earnings as an RN. A professional evaluation is usually necessary if this is to be a litigated point.