Engine Thermocouple
 

Thermocouple in engine works by hot and cold junction
the hot junction will be located at the engine
where will the cold junction be in large aircraft ?
I am sure cold junction will not located at the cockpit but then how cold junction get indication ?

I believe it the end connected to the junction box near the turbine section (engine area), Place might be different depending on the engine. From there it transferred to EEC/FADEC where true temperature adjustment its calculated (internally)

Bare in mind that the thermocouples produce MilliVolts of energy.