Which software can be used to measure the laptop heatsink (not cpu) temperature near the fan? Are there any alternate methods to measure the heat sink temperature (experimental or software based or by calculation)? Any website which might provide me charts/graphs/relations between cpu temperature or fan speed and heat sink temperature? Just to estimate, what is the general heatsink temperature? In my case, the cooling fan starts running when cpu reaches 66.8 degree C, so what can the heat sink temperature be after the fan has been running for say half an hour?
First you'd need a heat sink with a sensor. Then the software would need to be something designed to work with that sensor and a device that sensor connects to possibly. They do make wireless heat sensors you could check out. I goggled it but making direct recommendations isn't allowed in these forums.
Being it is a heat disapation device though the temperature from the part touching the cpu to the part furthest away would be drastically diffrent because it's designed to disapate the heat.