As far as I can tell, there are two kinds of thermal sensors: "real" and synthetic ones. To get thermal sensor information, on iPhone 6s, we'll get something similar to the following
iPhone:~ root# cycript -p UserEventAgent
cy# hs = [HidSensors sharedInstance]
#"<HidSensors: 0x14de04210>"
cy# sensors = new Instance(hs->hidSensorKeys)
@["gas gauge battery","PMU tdev1","PMU tdev1","PMU tdev2","PMU tdev3","PMU tdev4","PMU tdev4","PMU tcal","PMU tjunc","PMGR SOC Die Temp Sensor0","Avg: PMGR SOC Die Temp Sensor0","Max: PMGR SOC Die Temp Sensor0","PMGR SOC Die Temp Sensor1","Avg: PMGR SOC Die Temp Sensor1","Max: PMGR SOC Die Temp Sensor1","PMGR SOC Die Temp Sensor2","Avg: PMGR SOC Die Temp Sensor2","Max: PMGR SOC Die Temp Sensor2","TCC Temp Sensor0","Avg: TCC Temp Sensor0","Max: TCC Temp Sensor0","TCC Temp Sensor1","Avg: TCC Temp Sensor1","Max: TCC Temp Sensor1","TCC Temp Sensor2","Avg: TCC Temp Sensor2","Max: TCC Temp Sensor2"]
cy# sensors.length
27
cy# synthSensors = new Instance(hs->synthSensorKeys)
@["FrontCameraDie","RearCameraDie","CGH7Skin","CGLEDHSSkin","CGCenterSkin","BCH7Skin","BCLEDSkin","BCRadioSkin","CGRCAMSkin"]
cy# synthSensors.length
9
cy# tgs = [TGraphSampler sharedInstance]
#"<TGraphSampler: 0x14de31e80>"
cy# tgs->productObj->_totalSensorCount
36On iPhone 6, you'll get 23 sensros and 10 synthetic sensors.
cy# sensors = new Instance(hs->hidSensorKeys)
@["gas gauge battery","PMU FH","PMU RCAM","PMU PA","PMU SoC","PMU tbat","PMU tcal","PMU tjunc","PMGR SOC Die Temp Sensor0","Avg: PMGR SOC Die Temp Sensor0","Max: PMGR SOC Die Temp Sensor0","PMGR SOC Die Temp Sensor1","Avg: PMGR SOC Die Temp Sensor1","Max: PMGR SOC Die Temp Sensor1","TCC Temp Sensor0","Avg: TCC Temp Sensor0","Max: TCC Temp Sensor0","TCC Temp Sensor1","Avg: TCC Temp Sensor1","Max: TCC Temp Sensor1","TCC Temp Sensor2","Avg: TCC Temp Sensor2","Max: TCC Temp Sensor2"]
cy# synthSensors = new Instance(hs->synthSensorKeys)
@["FrontCameraDie","RearCameraDie","CGH7Skin","CGLEDHSSkin","CGCenterSkin","BCH7Skin","BCLEDSkin","BCRadioSkin","CGRCAMSkin","CGLEDSkin"]
cy# sensors.length
23
cy# synthSensors.length
10