This quest is not available in game.
Krakle in Un'Goro Crater wants you to find the hottest area of Fire Plume Ridge.
Whenever you find a hot spot, right click the thermometer to check the temperature. Keep looking until you find the hottest one.
The hot springs here are a source of mystery to me. Where does the heat come from?
Looking at how close the pools are to Fire Plume Ridge, I really wonder if the volcano might have something to do with it. I created a thermometer to take readings of the temperatures at the volcano, and I'd like to find the hottest part. It gives the measurements in degrees Kraklenheit!
Here, take it, and take readings of the temperatures at the ridge whenever you see a hot spot!