does the iphone 6s no sim use cdma or gsm

An iPhone 6S without a SIM doesn't do much of anything. You can't activate an iPhone without a SIM. An unlocked iPhone should work on any GSM/LTE carrier. A carrier with a legacy CDMA network might or might not accept an unlocked phone not intended for use on their network. Although there's no technological reason the phone won't work, it would depend on whether or not the carrier would add the phone to its database. Verizon, which is a CDMA/LTE carrier, will accept an unlocked iPhone.

If you have questions about whether an unlocked phone will work on your carrier of choice, ask them.

Best of luck.