Does NG4W2LL/A (iphone 6)support CDMA

What you have is a replacment model of this phone that was sold at Best Buy.

https://www.bestbuy.com/site/apple-iphone-6-64gb-space-gray-at-t/7640035.p?skuId =7640035

It does technically support CDMA as well as GSM as do all iPhone 6 models.

That does not mean it will work on every or any CDMA carrier for 2 separate reasons.

The first is that CDMA carriers like Sprint whitelist by IMEI which means they only allow a subset of all phones that can work on their network to actually operate there.

The second is the activation policy on the device and that can prevent the phone from provisioning for voice and SMS on CDMA even though LTE will work.

The bottom line is you may have two problems: 1) Sprint may not allow the phone on its network (you can run the IMEI to see if it is eligible) and 2) the phone may not have the correct activation policy even if Sprint does allow it.

As a practical matter, it probably is best to accept that you probably will not be able to get this phone to work on Sprint.